Position input device and computer system

ABSTRACT

A position input device is provided in which signals are transmitted from a position indicator, and signals transmitted from the position indicator are received by a position detector device. According to certain embodiments, an electrical double-layer capacitor, a charging circuit which charges the electrical double-layer capacitor, and a power transmission unit which relays and supplies to the charging circuit power supplied from a power supply unit external to the position indicator, are provided in the position indicator. In other embodiments the position input device has a built-in power supply unit, transmitting units, and a control unit for switching the transmitting units between energized and de-energized states. Also provided are position input systems and computer systems including the position input device, and methods of operating the position input device and the systems.

CROSS-REFERENCES TO RELATED APPLICATIONS AND CLAIM TO PRIORITY

The present application claims the benefit of Japanese Application No.P2005-357965, filed on Dec. 12, 2005, which application is incorporatedherein by reference and to which priority is claimed.

The present application also claims the benefit of Japanese ApplicationNo. P2006-073102 filed on Mar. 16, 2006, which application isincorporated hereby by reference and to which priority is claimed.

FIELD OF THE INVENTION

Aspects of this invention relate to a battery-free position pointingdevice (also referred to herein as a position indicator), a positioninput system, and a computer system which detect position bytransmitting and receiving signals between the position indicator andthe position detection device, and to related methods.

Additional aspects of the present invention relate to a positionpointing device with a built-in power source, a position input system,and a computer system suitable for use in detecting position, preferablyby electromagnetic induction, and preferably in a manner in which theservice life of the built-in power supply of the position pointingdevice is prolonged.

BACKGROUND OF THE INVENTION

Position input systems, also known as pen tablets or tablet/digitizers,have seen widespread use as input devices for computers, for example.The position input system generally comprises a pen-type or stylus-typeposition indicator (also referred to herein as a position pointingdevice) for indicating a position on a tablet, and a position detectiondevice. In such a position input system signals transmitted from theposition indicator are received by the position detection device todetect the position on the tablet indicated by the position indicator.So far various technologies have been developed for detecting theposition designated on the tablet. Of these various kinds of developedtechnologies, an electromagnetic induction system position detectingapparatus like the invention described in Japanese Published PatentApplication No. 2-53805 is known for detecting the position designatedon the tablet.

In recent years, position input systems have appeared which areintegrated with a liquid crystal display device, and which enableoperation of the position indicator on a display screen. Generally insuch a position input system, electric waves are transmitted to theposition indicator from the position detector device integrated with thedisplay screen, and these electric waves are utilized to transmitsignals from the position indicator. In such a position input system,because the signals transmitted from the position indicator to theposition detection device are comparatively weak, the sensitivity andprecision of the position detector device may be reduced in anenvironment of intense electromagnetic noise, such as may be generatedby the liquid crystal display device or other sources. As acountermeasure, the signals transmitted from the position detectordevice may be strengthened. However, strengthening of the signals isproblematic inasmuch as power consumption by the position detectordevice is increased.

It has been proposed to incorporate a battery into the positionindicator, so that the transmission of signals from the positiondetector device becomes unnecessary. Using such a method, strong signalscan be transmitted from the position indicator with low powerconsumption.

However, the use of batteries can also raise problems. In the case ofthe above-described position indicator, replacing the battery is timeconsuming and troublesome. Also, if the intensity of signals transmittedfrom the position indicator is to be increased, power consumption isincreased and battery depletion occurs in a short length of time, sothat the batteries built into the position indicator may need to bereplaced frequently, causing further inconvenience. In addition, theweight of a position indicator incorporating a battery is increasedsignificantly, and there is the further problem that operatingproperties are severely degraded.

Recently, it has been known to provide position pointing devices withtuning circuits at both ends of their pen-like bodies. The tuningcircuit at the first end is able to transmit written information, andthe tuning circuit at the other or second end is able to transmit otherinformation, such as the erasing of information. See Japanese PublishedPatent Application No. 8-96350. It has been proposed to provide suchposition pointing devices with built-in power supply units andoscillation units to increase the magnitude of transmission output, andthereby improve accuracy in detecting position. See Japanese PublishedPatent Application No. 10-214148.

However, if a position pointing device possesses a built-in power supplyunit (i.e., a battery) and a plurality of oscillation units instead ofthe above-discussed tuning circuits, then power consumption of thebuilt-in power supply unit is increased by a multiple equal to thenumber of oscillation units in the position pointing device, e.g., ifthe position pointing device contains two oscillation units, then powerconsumption is doubled. Accordingly, the time period during which theposition pointing device may be operated prior to consumption of all ofthe power in the built-in power supply is lessened correspondingly. As aresult, the battery must be replaced or recharged more frequently,inconveniencing the operator.

SUMMARY OF THE INVENTION

Aspects of this invention were devised in light of the abovecircumstances, and certain aspects have as an object the provision of aposition indicator device capable of stable position detection withoutreadily being affected by external noise even under low powerconsumption, which is lightweight, and which does not require batteryreplacement. It is another object of the invention to provide a positioninput system and a computer system to which this position indicatordevice is applied.

A first aspect of the invention provides a position input systemcomprising a position indicator for transmitting signals and a positiondetector device for receiving the signals transmitted from the positionindicator. The position indicator comprises an electrical double-layercapacitor, a charging circuit to charge the electrical double-layercapacitor, and a power transmission unit to relay and supply thecharging circuit with power supplied from a power supply unit externalto the position indicator.

According to a preferred implementation of this first aspect of theinvention, signals can be transmitted using an electrical double-layercapacitor provided in the position indicator, so that there is greaterfreedom with respect to power consumption for signal transmission. Forexample, compared with a case in which signals are transmitted to theposition indicator from the position detector device, according to thisimplementation of the first aspect of the invention signals transmittedfrom the position indicator can be more reliably detected by theposition detector device even at extremely low power consumption, thuspermitting power consumption by the position detector device to begreatly reduced. As a result, signals are transmitted reliably from theposition indicator to the position detector device with low powerconsumption and without easily being affected by external noise.Further, strong signals can be reliably received within the positiondetector device, so that the position indicated by the positionindicator can be detected.

Further, by using an electrical double-layer capacitor, short-durationcharging is possible, and a position indicator with the advantages oflight weight and compactness can be realized. That is, the positionindicator of the position input system of this aspect of the inventiondiffers from a position indicator incorporating a primary battery inthat troublesome and time-consuming battery replacement is not required.Further, because charging is possible in an extremely short time, thereis little inconvenience arising from an inability to use the positionindicator until charging is complete. The light weight of the positionindicator also affords excellent operating properties.

According to another implementation of this first aspect of theinvention, the position input system further comprises an external powersupply unit. The inclusion of the external power supply unit providesvarious benefits, such as the simplification of charging of theelectrical double-layer capacitor, and enhancement of the usability ofthe system.

According to another implementation of this first aspect of theinvention, a coil is provided in the position indicator, and an ACmagnetic field generation unit is provided as the power supply unit. Inthis case, by using the AC magnetic field generation unit to generate amagnetic field, an induced current flows in the coil, causing theelectrical double-layer capacitor to be charged. Power can be suppliedthrough this magnetic field without requiring contact, so that freedomof design of the position indicator is enhanced, and the durability ofthe position indicator and the power supply unit can be improved.

According to still another implementation of this first aspect of theinvention, as the power supply unit, the AC magnetic field generationunit is provided in a stand in which the position indicator can be set.By setting the position indicator in the stand, the electricaldouble-layer capacitor can be charged, so that operation related tocharging becomes extremely simple, and operability is improved.

According to yet another implementation of this first aspect of theinvention, a power supply assistance unit for receiving power from theelectrical double-layer capacitor and supplying a prescribed voltage tothe position indicator is provided in the position indicator. Thevoltage across the terminals of the electrical double-layer capacitor ishigh immediately after charging, and is expected to decline as power isconsumed. The power supply assistance unit preferably is operable tosupply a prescribed voltage based on the power of the electricaldouble-layer capacitor, so that when various circuitry is incorporatedinto the position indicator, stable operation of the circuitry isassured.

According to a further implementation of this first aspect of theinvention, the position detector device detects signals transmitted fromthe position indicator based on a static coupled state with the positionindicator. Moreover, the position detector device may be a device whichdetects signals transmitted from the position indicator based onelectromagnetic coupling with the position indicator. Further, theposition indicator may employ a configuration comprising a resonancecircuit comprising a coil and a capacitor.

According to still a further implementation of the first aspect of theinvention, the position indicator comprises a voltage detection unit andan information transmission unit. The voltage detection unit detectswhen the voltage of the electrical double-layer capacitor has fallen toor below a prescribed voltage value. The information transmission unittransmits information indicating detection by the voltage detection unitof the fallen voltage to the position detector device. The transmissionof this information allows the position detector device to automaticallydetect and notify the user of the need for charging.

It should be understood that the above implementations of the firstaspect may be practiced in various combinations.

According to a second aspect of the invention, a computer system isprovided. The computer system comprises a position input system, adisplay device for displaying screens, and a computer for processinginformation based on positions detected by the position input system.The position input device comprises a position indicator which transmitssignals, and a position detector device which receives signalstransmitted from the position indicator. The position indicator containsan electrical double-layer capacitor, a charging circuit for chargingthe electrical double-layer capacitor, and a power transmission unit forrelaying and supplying the charging circuit with power supplied from apower supply unit external to the position indicator.

According to the second aspect of the invention, preferably signals canbe transmitted using the electrical double-layer capacitor provided inthe position indicator. As a consequence, power consumption for signaltransmission is greatly reduced, and the position indicator may beoperated without significant impediment from external noise. In thissystem, the time and trouble otherwise that would be involved in thereplacement of a battery in the position indicator may be avoided.Moreover by using the electrical double-layer capacitor, the positionindicator can be charged in an extremely short time. Further, theposition indicator can be made lightweight, for excellent operability.

According to an implementation of the second aspect of the invention,the position indicator may further include a voltage detection unitwhich detects when the voltage of the electrical double-layer capacitorhas fallen to or below a prescribed voltage value, and an informationtransmission unit which transmits to the position detector deviceinformation indicating detection by the voltage detection unit of thefallen voltage.

According to this implementation of the second aspect of this invention,the need to charge the position indicator may be detected in theposition detector device when the voltage of the electrical double-layercapacitor in the position indicator has fallen below the prescribedvoltage value, and the position indicator can be recharged.

According to another implementation of this second aspect of theinvention, the computer system further comprises an AC magnetic fieldgeneration unit as the power supply unit, and a coil is provided in theposition indicator. The computer is operable to use the positiondetector device to receive information transmitted by the informationtransmission unit provided in the position indicator. When, based on theinformation from the information transmission unit, it is determinedthat the electrical double-layer capacitor must or should be charged,current is supplied to the AC magnetic field generation unit.

In this implementation, current is supplied to the AC magnetic fieldgeneration unit which charges the electrical double-layer capacitor ofthe position indicator only when the information transmission unitreports the drop in the voltage of the electrical double-layercapacitor. Power consumption can be thereby rendered efficient byavoiding the unnecessary supply of current to the AC magnetic fieldgeneration unit, i.e., when the voltage of the electrical double-layercapacitor has not fallen. In addition, charging can be performed rapidlywhen necessary.

According to another implementation of this second aspect of theinvention, the computer is operable to determine, based on informationtransmitted from the position indicator and received by the positiondetector device, whether the electrical double-layer capacitor must orshould be charged, and to cause a report to be generated and displayedby the display device. The report may notify the user that the positionindicator requires charging, so the user views the report and performscharging. Thus, the user can concentrate on operation of the devicewithout paying special consideration to the timing of charging, forgreater convenience to the user.

According to still another implementation of this second aspect of theinvention, the computer system further comprises an AC magnetic fieldgeneration unit employed as the power supply unit, with a coil providedin the position indicator. The computer is operable to supply current tothe AC magnetic field generation unit when a prescribed time has elapsedfrom the previous supply of current to the AC magnetic field generationunit. According to a preferred practice of this implementation, afterthe AC magnetic field generation unit is supplied with current, anestimated timing value is determined to anticipate a drop in the voltageof the electrical double-layer capacitor. Current is again supplied tothe AC magnetic field generation unit upon expiration of the estimatedtiming value. In this manner, power consumption can be renderedefficient, without unnecessarily supplying unneeded current to the ACmagnetic field generation unit. In addition, charging can be performedrapidly when necessary. Further, current can be supplied to the ACmagnetic field generation unit with appropriate timing withoutperforming complex processing, thereby enabling transition to thecharged state.

According to yet another implementation, a configuration may be employedin which the computer system further comprises an AC magnetic fieldgeneration unit as the power supply unit, with a coil provided in theposition indicator. According to this implementation, current issupplied to the AC magnetic field generation unit within a timing whichanticipates a drop in the voltage of the electrical double-layercapacitor, without waiting for transmission of information from theposition indicator. More specifically, the computer causes current to besupplied to the AC magnetic field generation unit during the intervalbefore or when a prescribed time has elapsed from the previous supply ofcurrent to the AC magnetic field generation unit, even if the positiondetector device has not yet received information indicating detection ofthe voltage drop transmitted from the information transmission unitprovided in the position indicator. Accordingly, charging can beperformed rapidly when necessary, for example, even when for example thevoltage across the electrical double-layer capacitor drops sharply andthe above information cannot be transmitted to the position detectordevice.

According to additional implementations of this second aspect of theinvention, the computer system comprises a prompt for notifying theoperator to charge the electrical double-layer capacitor. The prompt maybe located on the position indicator, position detector device, and/orthe power transmission unit.

According to yet an additional implementation of the second aspect, thepower supply unit is integrated on or into the position detector deviceto form a unitary piece.

It should be understood that the above implementations of the secondaspect may be practiced in various combinations.

According to a third aspect of the invention, a method is provided forcharging a position indicator of a position input system, whichcomprises a position indicator for transmitting signals and a positiondetector device for receiving signals transmitted by the positionindicator. The position indicator includes an electrical double-layercapacitor, a charging circuit which charges the electrical double-layercapacitor, and a power transmission unit. Power is supplied from a powersupply unit external to the position indicator, and the powertransmission unit relays the power to the charging circuit.

A fourth aspect of the invention provides a method of operating acomputer system. A position input system comprises a position indicatorfor transmitting signals, a position detector device for receivingsignals transmitted from the position indicator is provided, and acomputer for processing information based on positions detected by saidposition input system. Power is supplied from a power supply unitexternal to the position indicator, and the power transmission unitrelays the power to the charging circuit.

According to an implementation of this fourth aspect of the invention,the method further comprises detecting when the voltage of theelectrical double-layer capacitor has dropped to or below a prescribedvoltage value, and transmitting to the position detector deviceinformation indicating detection of the voltage drop.

Advantageously, in preferred aspects and implementations of thisinvention described above, an electrical double-layer capacitor servesas a power storage of the position indicator, so that there is no needto supply power to the position indicator from the position detectordevice. Strong signals can be received from the position indicator bythe position detector device with low power consumption and withouteasily being affected by external noise. Further, no time or troubleneed be taken to replace batteries in the position indicator, andcharging can be performed in an extremely short time. Moreover, theelectrical double-layer capacitor is lighter than ordinary batterieswhile affording high capacity, so that the position indicator enjoys theadvantages of light weight and excellent operability. As a result, aposition input system comprising a position indicator with light weightand excellent operability, as well as a computer system comprising theposition input system, can be realized.

Another object of the present invention is to provide a positionpointing device having a built-in battery, a position input systemcomprising a position pointing device having a built-in battery and aposition detecting apparatus, and a computer system possessing one ormore of the following advantages: an efficient power consumption, evenwhen a plurality of oscillation units is provided; and a lower frequencyof operational disruptions (e.g., battery changes and recharges) than isencountered relative to conventional devices containing a built-inbattery.

A fifth aspect of the invention is directed to a position pointingdevice for transmitting a positioning signal to a position detectingtablet. The position pointing device includes a built-in power supplyunit, signal transmitting units provided at a plurality of portions ofthe position pointing device, and a control unit for switching thesignal transmitting units between energized or de-energized states.

According to an exemplary implementation of this fifth aspect of theinvention, the plurality of signal transmitting units includes first andsecond signal transmitting units respectively provided at opposite endportions of the position pointing device, preferably to transmit apen-point signal and an eraser signal, respectively.

In another implementation of the position pointing device of the fifthaspect of the invention, the control unit alternately switches thesignal transmitting units between the energized and de-energized states.

According to still another implementation of the fifth aspect of theinvention, the position pointing device further includes a directiondetecting unit for detecting the direction in which the positionpointing device is arranged relative to the position detecting tablet.The control unit is operable to energize whichever of the signaltransmission units faces the position detecting tablet based on adetected result of the direction detecting unit.

According to still another implementation of the position pointingdevice of the fifth aspect of the invention, the direction detectingunit is a stylus pressure detecting unit and the control unit isoperable to energize whichever of the signal transmission units isdetermined to be in use based on detection by the stylus pressuredetecting unit of a load greater than a predetermined load. At the sametime, preferably the control unit de-energizes the signal transmissionunit determined not to be in use.

In further implementation of the fifth aspect of the invention, thecontrol unit is operable to sequentially operate the plurality of signaltransmitting units if it is determined by the stylus pressure detectingunit that a load greater than the predetermined load is not detectedfrom any one of the signal transmitting units.

In still a further implementation of the fifth aspect of the invention,the direction detecting unit is a touch-sensitive sensor and the controlunit is operable to energize whichever of the signal transmission unitsis associated with an end of the position pointing device which touchesthe position detecting tablet. Preferably, the control unit de-energizeswhichever of the signal transmission units is associated with an end ofthe position pointing device which does not touch the position detectingtablet.

It should be understood that the above implementations of the fifthaspect of the invention may be practiced in various combinations.

A sixth aspect of the invention is directed to a position pointingdevice for transmitting a positioning signal to a position detectingtablet. This position pointing device includes a built-in power supplyunit, a plurality of signal transmitting units provided at a pluralityof portions of the position pointing device, and a power control unitfor switching magnitude of transmission power of said signaltransmitting units between at least two levels.

In accordance with an implementation of the sixth aspect of theinvention, first and second signal transmitting units of the pluralityof signal transmitting units are respectively provided at opposite endportions of the position pointing device to transmit a pen-point signaland an eraser signal, respectively.

In the position pointing device according to another implementation ofthe sixth aspect of the invention, the position pointing device furtherincludes a direction detecting unit for detecting the direction of theposition pointing device relative to the position detecting tablet. Thepower control unit is operable to increase, based on a detected resultof the direction detecting unit, a magnitude of transmission power fromwhichever of the signal transmitting units is located on a side of theposition pointing device nearer to the position detecting tablet, sothat the magnitude of transmission power from the signal transmittingunit located on the side nearer to the position detecting tablet isgreater than the magnitude of transmission power from whichever of thesignal transmitting units is on the opposite side of the positionpointing device.

A seventh aspect of the invention is directed to a position input systemincluding a position pointing device for transmitting positioninginformation signals. The position pointing device includes a built-inpower supply unit, a plurality of signal transmitting units provided ata plurality of portions of the position pointing device, and a powercontrol unit for controlling the transmission power of each of aplurality of signal transmitting units. The position input systemfurther includes a position detecting tablet for receiving thepositioning signals from the position pointing device. A discriminatingunit discriminates the signals from the signal transmitting units.

In an exemplary implementation of the position input system of theseventh aspect of the invention, the discriminating unit is a firstdiscriminating unit provided at a first end portion of the positionpointing device to discriminate a pen-point signal, and the positioninput system further includes a second discriminating unit provided at asecond end portion of the position pointing device for discriminating aneraser signal.

The eighth aspect of the present invention is directed to a computersystem including a position pointing device for transmitting positioningsignals. The position pointing device includes a built-in power supplyunit, a plurality of signal transmitting units provided at a pluralityof portions of the position pointing device, and a power control unitfor controlling transmission power of each of a plurality of signaltransmitting units. The computer system further includes a positiondetecting tablet for receiving positioning signals from the positionpointing device. A discriminating unit discriminates the signals from aplurality of signal transmitting units. A computer is provided forprocessing the positioning information from the position pointing deviceand discrimination information from the discriminating unit.

In an exemplary implementation of the system of the eighth aspect of theinvention, the discriminating unit is a first discriminating unitprovided at a first end portion of the position pointing device todiscriminate a pen-point signal, and the system further includes asecond discriminating unit provided at a second end portion of theposition pointing device for discriminating an eraser signal.

A ninth aspect of the invention provides a method for charging aposition pointing device used for transmitting a positioning signal to aposition detecting tablet. The position pointing device comprises abuilt-in power supply unit, a plurality of signal transmitting unitsprovided at a plurality of portions of the position pointing device, anda control unit. The control unit switches the plurality of signaltransmitting units between energized or de-energized states.

According to the position pointing device, the position detectingapparatus, the computer system, and method encompassed in the fifth toninth aspects of the present invention, the position pointing device hasa built-in power supply unit so that accuracy in detecting position canbe improved. Even when the position pointing device includes a pluralityof oscillation circuits, power consumption by the position pointingdevice can be reduced. Also, the battery change and recharge frequencycan be reduced, and the position detecting apparatus can be used withoutsignificant interruption.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part ofthe specification. The drawings, together with the general descriptiongiven above and the detailed description of the preferred embodimentsand methods given below, serve to explain the principles of theinvention. In such drawings:

FIG. 1 is a simplified diagram of a system of a first embodiment of theinvention;

FIG. 2 is an oblique view of a position indicator;

FIG. 3 is an electrical diagram of an internal circuit incorporated in aposition indicator;

FIG. 4 is an electrical diagram of an internal circuit incorporated in atablet;

FIG. 5 is a timing chart illustrating transmission operation by aposition indicator, in which (A) illustrates the output from terminal P0of a controller, (B) illustrates the voltage across the terminals of aresonance circuit, (C) shows the operating state, and (D) shows data;

FIG. 6A is an oblique, cross-sectional view of a charger, and FIG. 6B isa functional block diagram for the charger;

FIG. 7 is a functional block diagram showing the configuration of thecontrol system of a computer main unit;

FIG. 8 is a flowchart showing charging control processing executed inthe computer main unit;

FIG. 9 illustrates an example of a charge request message displayed on amonitor during charging control processing;

FIG. 10A shows an example of a light-emitting portion on a positionindicator;

FIG. 10B shows an example of a light-emitting portion on a tablet;

FIG. 10C is a cross-sectional view of a light-emitting portion on acharger;

FIG. 11 is a flowchart illustrating charging control processing in amodified example of the first embodiment;

FIG. 12 is a flowchart illustrating charging control processing inanother modified example of the first embodiment;

FIG. 13A is an oblique, cross-sectional view of a charger of a secondembodiment of the invention, and FIG. 13B is a functional block diagramfor the charger;

FIG. 14 is an oblique view illustrating the tablet of a third embodimentof the invention;

FIG. 15 is an oblique view of a tablet of a fourth embodiment of theinvention;

FIG. 16 illustrates a tablet-type computer of a fifth embodiment of theinvention;

FIG. 17 is a diagram of the internal circuitry of a position indicatorof a sixth embodiment of the invention;

FIG. 18 is a diagram of the internal circuitry of a tablet of the sixthembodiment of the invention;

FIG. 19 is an electrical block diagram illustrating a position pointingdevice according to a seventh embodiment of the present invention;

FIG. 20 is an electrical block diagram showing illustrating a positionpointing device according to an eighth embodiment of the presentinvention;

FIG. 21 is a perspective, fragmentary cross-sectional view of a positionpointing stylus pen serving as the above-mentioned position pointingdevice of the eighth embodiment of the present invention;

FIGS. 22A, 22B, and 22 c are diagrams of waveforms of signals to whichreference will be made in explaining operations of the position pointingdevice according to the eighth embodiment of the present invention;

FIG. 23 is an electrical block diagram illustrating a position pointingdevice according to a ninth embodiment of the present invention;

FIGS. 24A and 24B are waveform diagrams of signals to which referencewill be made in explaining operations of the position pointing deviceaccording to the ninth embodiment of the present invention;

FIG. 25 is a perspective view of a position pointing stylus pen servingas the above-mentioned position pointing device according to the ninthembodiment of the present invention;

FIG. 26 is an electrical block diagram illustrating a position pointingdevice according to a tenth embodiment of the present invention; and

FIG. 27 is an electrical block diagram illustrating a position detectingapparatus and a computer according to an eleventh embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) AND PREFERREDMETHOD(S)

Reference will now be made to the presently preferred embodiments andmethods of the invention as illustrated in the accompanying drawings, inwhich like reference characters designate like or corresponding partsthroughout the drawings. It should be noted, however, that the inventionin its broader aspects is not limited to the specific details,representative devices and methods, and illustrative examples shown anddescribed in this section in connection with the preferred embodimentsand methods. The invention according to its various aspects isparticularly pointed out and distinctly claimed in the attached claimsread in view of this specification, and appropriate equivalents.

First Embodiment

FIG. 1 shows an overview of a computer system 10 of a first embodimentof the invention.

In computer system 10 shown in FIG. 1, a monitor 12 and a keyboard 13are connected to a computer main unit 11. An LCD (Liquid CrystalDisplay) or other display screen is integrated with a tablet 20 into themonitor 12 to perform position input using a position indicator 30, suchas a pen. In addition, a charger 50, as best shown in FIG. 6A as a standor holder, to charge the position indicator 30, described below, isconnected to the computer main unit 11.

The tablet 20 (position detector device) functions as part of a positioninput system through use in conjunction with the position indicator 30,and detects a position indicated by the position indicator 30 on aninput area 20A of the screen of the monitor 12, and outputs information,e.g., the position coordinates to the computer main unit 11.

The charger 50 is used to charge the position indicator 30, and issupplied with power by the computer main unit 11.

FIG. 2 shows an external view of the position indicator 30. A core 32protrudes from the tip of a case 31. Two switches 33, 34 are positionedon a side face of the case 31, and an internal circuit 40, as best shownin FIG. 3, to transmit signals to the tablet 20 is housed within thecase 31.

The switches 33, 34 illustrated in FIG. 2 are represented by the samereference numerals, i.e., 33 and 34, respectively, in the diagram of theinternal circuit 40, as illustrated in FIG. 3. The core 32 shown in FIG.2 is linked to a variable-capacitance capacitor 425 in the internalcircuit 40, as best shown in FIG. 3. While the position indicator 30 isused in operations in the display area (input area 20A) of the monitor12, when pressure is applied to the core 32, the pressure on the core 32is transmitted to the variable-capacitance capacitor 425, and thecapacitance of the variable-capacitance capacitor 425 changes accordingto the magnitude of the pressure. The switches 33, 34 are operated bythe user as desired.

FIG. 3 shows the configuration of the internal circuit 40 of theposition indicator 30. The internal circuit 40 comprises a controller(microprocessor) 401, and operates according to a prescribed program. InFIG. 3, an oscillator 421 generates a clock signal to cause operation ofthe controller 401.

A resonance circuit 410 resonates at a prescribed frequency, and isconnected via a capacitor 406 to the terminal P0 of the controller 401.A signal with the same frequency as the resonance frequency of theresonance circuit 410 is output from the terminal P0 of the controller401 with timing as best shown in FIG. 5, to cause radiation of an ACmagnetic field from the resonance circuit 410. An electricaldouble-layer capacitor 403 supplies power to the controller 401 via aswitch 404. A capacitor 405 stabilizes the voltage supplied to thecontroller 401. An aluminum electrolytic capacitor of a value of, forexample, several tens to several hundreds of microfarads is appropriatefor capacitor 405.

A voltage detector 407 detects whether the voltage across the capacitor405 is equal to or greater than a prescribed value, which in thisembodiment is 1.8 V, although other values may be used. If the voltageis 1.8 V or higher, a high level voltage (e.g., a voltage substantiallyequal to the voltage across the capacitor 405) is output. If the voltageis less than 1.8 V, a low level voltage (e.g., 0 V) is output. Theswitch 404 is switched to the “on” state or the “off” state by a controlsignal output from terminal P2 of the controller 401. As with anordinary capacitor, the voltage held by the electrical double-layercapacitor 403 declines with discharge. In order to hold constant thelevel of the AC magnetic field transmitted from the resonance circuit410, the level of the signal output from terminal P0 of the controller401 is held constant, and, to this end, the power supply voltage of thecontroller 401, that is, the voltage across the capacitor 405, is heldconstant. To achieve this, in the present embodiment, a power supplyassistance unit, described below, is used.

The controller 401 repeats the operation to transmit signals fromterminal P0 with the timing shown in FIG. 5. By detecting the presenceor absence of signals from terminal P1 periodically during thisinterval, the voltage across the capacitor 405 is evaluated to determinewhether it is at 1.8 V or higher. When the voltage is less than 1.8 V,the controller 401 outputs a control signal from terminal P2, and turnsswitch 404 on for a prescribed time (for example, approximately 1 μs toapproximately 80 μs). If a voltage higher than 1.8 V is held by theelectrical double-layer capacitor 403, then a portion of the charge heldby the electrical double-layer capacitor 403 moves via the switch 404 tothe capacitor 405, and so the voltage of the capacitor 405 rises to 1.8V or higher. By thus periodically monitoring the terminal P1, the of thecapacitor 405 remains substantially in the vicinity of 1.8 V. As thevoltage on the electrical double-layer capacitor 403 approaches 1.8 V,the above-described operation causes the extent of the increase in thevoltage of the capacitor 405 to become smaller, and the switch 404 isturned on more frequently. When this turning-on occurs at a frequencyequal to or greater than a fixed value (for example, once every twotimes monitored), the controller 401 adjusts the time over which theswitch 404 is turned on to be somewhat longer.

According to the above-described operation, the power supply voltage ofthe controller 401 in this embodiment is always held at a fixed value,so that the strength of signals transmitted from the resonance circuit410 can be held constant. Further, unnecessary increases in the powersupply voltage of the controller 401 are avoided, so there is thefurther advantage that current consumption is reduced.

A determination that the voltage on the electrical double-layercapacitor 403 has fallen close to 1.8 V may be drawn if the time whichthe switch 404 is turned on is set to a long value (for example, 80 μs),and the frequency with which the switch 404 is turned on reaches orexceeds a constant value (for example once every two times monitored).Under these circumstances, the controller 401 transmits information (acharging request) indicating that the power supply voltage of theposition indicator 30 has fallen, as indicated by the operation of FIG.5.

When a charging request indicating that the power supply voltage hasfallen is transmitted from the position indicator 30, notification isprovided to the user by an operation described below. Upon receiving thenotification, the user knows to mount the position indicator 30 in thecharger 50.

FIG. 6A shows an oblique, cut-away view of the configuration of thecharger 50 connected to the computer main unit 11. FIG. 6B is afunctional block diagram for operation of the charger 50. An insertionopening 52 provides access to an area into which the position indicator30 is inserted. A support portion 53 supports the position indicator 30.A power supply coil 54 is wound about the support portion 53. The powersupply coil 54 is connected to a charging control circuit 55, and thecharging control circuit 55 is connected to the computer main unit 11.The charging control circuit 55 generates an AC voltage at the samefrequency as the resonance frequency of the resonance circuit 410 bymeans of power supplied by the computer main unit 11, and applies the ACvoltage to the power supply coil 54. In this manner, an AC magneticfield is generated in the hollow portion of the support portion 53.

When the position indicator 30 is inserted into the insertion opening 52of charger 50, an induced voltage occurs in the resonance circuit 410 ofthe position indicator 30. This induced voltage is rectified by a diode402, as best shown in FIG. 3, causing the electrical double-layercapacitor 403 to be charged.

The position indicator 30 and the charger 50 which operate as explainedabove contain the following circuits and units: a charging circuitformed by the resonance circuit 410 and the diode 402; an informationtransmission unit formed by the resonance circuit 410, controller 401and capacitor 406; a voltage detection unit formed by the voltagedetector 407 and controller 401; a power supply assistance unit formedby the capacitor 405, switch 404, voltage detector 407 and controller401; an AC magnetic field generation unit formed by the power supplycoil 54 and charging control circuit 55; and a power transmission unitformed by the resonance circuit 410.

In this embodiment, a power supply assistance unit is provided such thatoperation is always normal when the voltage across the electricaldouble-layer capacitor 403 is equal to or greater than the operatingvoltage (here 1.8 V) of the controller 401. By providing a configurationwhich causes the voltage across the electrical double-layer capacitor403 to be increased, a constant voltage can be supplied to thecontroller 401 even when voltage across the electrical double-layercapacitor 403 falls below the operating voltage of the controller 401.

FIG. 4 shows the internal configuration (tablet circuit 21) of thetablet 20. The tablet circuit 21 is a circuit which receives signalstransmitted from the internal circuit 40 (FIG. 3) of the positionindicator 30, and detects the position indicated by the positionindicator 30. The tablet circuit 21 includes a CPU (Central ProcessingUnit) 22 which exercises control over each of the components illustratedin FIG. 4.

As best shown in FIG. 4, 21A and 21B are loop coil groups, and areembedded in the input area 20A (FIG. 1) of the tablet 20. In the inputarea 20A, a virtual X-Y orthogonal coordinate system is set. The loopcoil group 21A comprises a plurality of loop coils arranged in the Xdirection, and the loop coil group 21B comprises a plurality of loopcoils arranged in the Y direction. Each of the loop coils comprised bythe loop coil groups 21A and 21B is connected to a selection circuit 23.The selection circuit 23 selects one loop coil from among the loop coilsof the loop coil groups 21A and 21B, according to control of the CPU 22.An amplifier 24 amplifies the signals received by the loop coilsselected by the selection circuit 23. A BPF (Band Pass Filter) 25 passesthe component of the signal amplified by the amplifier 24 in a specificfrequency band. The signal component passed by the BPF 25 is convertedinto a voltage by a detector circuit 26, and is input to a sample/holdcircuit (S/H) 27. The voltage held by the sample/hold circuit 27 isoutput to an AD conversion circuit (A/D) 28, and the CPU 22 reads thevalue output from the AD conversion circuit 28, and stores the value asthe level of the signal read from the position indicator 30.

FIG. 5 is a timing chart showing transmission operations by the positionindicator 30 to transmit signals to the tablet 20. In the figure, (A)illustrates output signals at terminal P0 of the controller 401, (B)illustrates signals of the resonance circuit 410, (C) indicates thestate of operation in the controller 401, and (D) shows the contents ofresponse data. The transmission operation shown in FIG. 5 broadlycomprises a continuous transmission interval (times T1 to T2), and adata response interval (T2 to T3).

In the continuous transmission interval from times T1 to T2, a signal isoutput intermittently for a prescribed time (for example 2 ms) or longerfrom terminal P0 of the controller 401. This prescribed time is set tobe sufficiently longer than the transmission time per bit of the dataresponse interval. Employing this continuous transmission operation, anAC magnetic field is radiated intermittently from the resonance circuit410 during the prescribed time. When the prescribed time elapses, thecontroller 401 halts output of the signal from terminal P0. Afterwaiting for a time, for example about 200 μs, until the resonancecircuit signal has attenuated and has substantially vanished, thecontroller 401 shifts into the operation of the data response interval(T2 to T3). In the data response interval, 300 μs are allocated to onebit; here, 12 bits of data are transmitted. When the response data is“0”, a signal is output for 100 μs from terminal P0, and output ishalted for the remaining 200 μs. When the response data is “1”, outputfrom terminal P0 is halted for 300 μs. The 12 bits of data comprise ninebits of a stylus pressure value, obtained when the controller 401detects the discharge time upon discharge through the resistance 424 ofthe variable-capacitance capacitor 425, as best shown in FIG. 3, thecapacitance of which changes according to pressure applied to the core32; two bits of switch information, resulting from detection of theoperation states of the switches 33 and 34; and the above-described onebit of charging request information.

Operation of the tablet circuit 21 when the position indicator 30,operating in this manner, is placed on the input area 20A of the tablet,is described below.

First, the CPU 22 detects the received signal level while switching inorder among single loop coils in the loop coil group 21B (indicatordetection step). Here, if the position indicator 30 is placed at aposition which is closest to, for example, loop coil Y7 among the loopcoil group 21B, then the CPU 22 detects the strongest signal level whenloop coil Y7 is selected. Next, the Y7 loop coil for which the strongestsignal level was detected is selected, and the CPU 22 detects the signallevel over a period which is short compared with the data responseperiod (300 μs) of the position indicator (continuous transmissiondetection step). Here, when a signal at or above a prescribed level isdetected continuously over a longer interval than the data responseperiod (300 μs), operation proceeds to the coordinate detection stepdescribed below.

When a signal is detected at or above a prescribed level, continuouslyover an interval longer than the data response period (300 μs), theposition indicator 30 has entered into the continuous transmissioninterval. A stabilized signal is radiated from the position indicator 30for a period of time.

The CPU 22 detects the approximate X-axis position in the input area20A. The CPU 22 detects the received signal level while switching andselecting in order one loop coil from among the loop coil group 21A(X-axis position detection step). Here, if the position indicator 30 isplaced in a position which is closest to the loop coil X14 of the loopcoil group 21A, then the CPU 22 detects the strongest signal level whenthe loop coil X14 is selected. Next, the CPU 22 detects the signal levelwhile switching in order between a plurality of (for example, five) loopcoils centered on X14 and Y7. Here, a strong signal is detected from theloop coils X14 and Y7 which are closest to the position indicator 30,and the further from these loop coils, the weaker is the signal. The CPU22 performs interpolation calculations between coils based on the signallevel distribution detected for the X axis and Y axis, to accuratelycalculate the indicated position in the input area 20A (coordinatecalculation step). The interpolation calculation is performed in amanner known in the art.

When the coordinate calculation step ends, the CPU 22 then proceeds to acontinuous transmission end detection step. The CPU 22 causes theselection circuit 23 to select Y7. In this state, the CPU 22 detects thesignal level continuously in periods as short as possible (for example,at 5 μs intervals). When continuous transmission by the positionindicator 30 ends, the signal from the resonance circuit 41 is graduallyattenuated. The CPU 22 detects the fact that the reception level hasfallen to or below a prescribed value, and detects the timing with whichcontinuous transmission ends. When the reception level falls to or belowthe prescribed value, the CPU 22 saves this time as the continuoustransmission end time, and then proceeds to a data reception step.

Based on the continuous transmission end time, the CPU 22 performssignal detection 12 times with the same period as the data responseperiod of the position indicator 30 (300 μs). In this signal detection,the delay time from the continuous transmission end time is adjusted inadvance such that detection occurs precisely when the signal generatedin the resonance circuit 410 when there is a data “0” response from theposition indicator 30 is maximum.

In accordance with the above-described operation, the 12 bits of datatransmitted from the position indicator 30 can be accurately detected bythe CPU 22 as the presence or absence of a detection signal.

FIG. 7 is a block diagram showing the functional configuration of thecontrol system 100 of the computer main unit 11.

The control system 100, as best shown in FIG. 7, comprises a CPU 101which executes a program to perform data computation processing; ROM(Read-Only Memory) 102 which stores programs, data and similar; RAM(Random Access Memory) 103 which temporarily stores programs executed bythe CPU 101, data and similar used in computation processing; a storageportion 104 which stores various data; an input portion 105, to which akeyboard 13 and the tablet 20 are connected; a display portion 106 towhich is connected the monitor 12; and an interface portion 107. Each ofthese portions is connected to a bus 108.

In this embodiment, the interface portion 107 is connected to externalequipment. In addition to performing functions to send and receivevarious data to and from the external equipment, the interface portion107 has a function of supplying power to external equipment. The charger50 is connected to the interface portion 107, and the interface portion107 supplies power to the charger 50 under control of the CPU 101.

Further, when a charging request, which requests charging of theposition indicator 30, is input from the tablet 20 via the input portion105, the CPU 101 executes charging control processing, as best shown inFIG. 8, in concert with the tablet 20 and charger 50, to cause chargingof the position indicator 30.

FIG. 8 is a flowchart showing charging control processing executed inthe system 10.

Charging control processing is started when the tablet 20 receivescharging request data “1” transmitted from the position indicator 30(step S1). As explained above, charging request data “1” is dataindicating that the position indicator 30 requests charging of theelectrical double-layer capacitor 403. Upon receiving the chargingrequest data “1”, the tablet 20 transmits a charging request to thecomputer main unit 11 (step S2).

The CPU 101, upon receiving the charging request from the tablet 20(step S3), displays a charging request message on the monitor 12 (stepS4). This charging request message is a message requesting that the useroperating the position indicator 30 set the position indicator 30 in thecharger 50 in order to allow charging to occur. The charging requestmessage may for example be displayed in a charging guidance screen 109as shown in FIG. 9.

Next, the CPU 101 causes the start of the supply of power to the charger50 from the interface portion 107 (step S5), and, after a prescribedtime has elapsed, causes the supply of power to the charger 50 to bestopped (step S6), and then returns to step S1.

In this way, the charger 50 generates an AC magnetic field in thevicinity of the coil 412 of the internal circuit 40 (FIG. 3), and thusthe electrical double-layer capacitor 403 is charged. Compared with aso-called secondary battery (nickel-cadmium battery or similar),charging of the electrical double-layer capacitor 403 is completed in anextremely short amount of time (for example, approximately 10 to 50seconds). Hence, the time required for supplying power to the charger 50from the interface portion 107, including the time required for the userto set the position indicator 30 in the charger 50, is about two toabout three minutes or so.

In charging control processing, when the voltage across the electricaldouble-layer capacitor 403 falls during use of the position indicator 30by the user, a display on the monitor 12 provides guidance to charge theposition indicator 30, so that the user can charge the positionindicator 30 according to this guidance. Charging of the positionindicator 30 is performed in a very short time simply by inserting theposition indicator 30 into the insertion opening 52 of the charger 50,so that the user performs only an extremely simple operation, withoutdiminution of operability.

In the position input system of this embodiment, signals are transmittedby power accumulated in the electrical double-layer capacitor 403.Compared with known devices in which signals are transmitted from thetablet, in the present embodiment strong signals can be received by thetablet 20 from the position indicator even under extremely low powerconsumption. Consequently, strong signals can be initiated by andreceived from the position indicator 30 even in the presence of noisefrom external sources, and in particular noise from an integrated LCD,so advantageously coordinate position and data can be detected withstability.

Further, the electrical double-layer capacitor 403 does not requirebattery replacement as in the case of known devices which incorporateprimary batteries. Moreover, charging can be performed in an extremelyshort time compared with other secondary batteries having comparablecapacities, so that the user is not inconvenienced for a prolongedperiod while the position indicator recharges.

When charging the electrical double-layer capacitor 403 of the positionindicator 30, charging can be performed extremely easily, merely bysetting the position indicator 30 in the charger 50. This charging isperformed by causing the power supply coil 54 of the charger 50 togenerate an AC magnetic field in the vicinity of the coil 402. The powersupply coils 54 and 412 do not make contact. As a result of thiscontact-free configuration, there is greater freedom of design of thecharger 50 and position indicator 30, and durability can be furtherenhanced.

In the above first embodiment, an example was explained in which, bydisplaying a charging guidance screen 109 or similar notification on themonitor 12 the user is prompted to perform charging. However, theinvention is not limited to such a configuration. For example, the needfor charging can be reported through the position indicator 30, tablet20, or charger 50. This reporting by the position indicator 30, tablet20 and charger 50 may be performed independently, or may be performed incombination with one another and optionally simultaneously, or may beperformed in place of a charging request message displayed on themonitor 12 in the above-described charging control processing, or may beperformed in conjunction with display of the charging request message.

For example, as best shown in FIG. 10A, a light-emitting portion 39 isprovided in the case 31 of the position indicator 30. When thecontroller 401 determines that charging of the electrical double-layercapacitor 403 is necessary, the light-emitting portion 39 is caused tolight or to flash under control of the controller 401. Thelight-emitting portion 39, for example, may be an LED (light-emittingdiode).

As another example, as shown in FIG. 10B, a light-emitting portion 29configured as an LED similarly to the light-emitting portion 39 may beprovided in the housing of the tablet 20. In this example, when thetablet receives a charging request data “1” transmitted from theposition indicator 30, the light-emitting portion 29 is caused to lightunder control of the CPU 22.

As a further example, as shown in FIG. 10C, a light-emitting portion 59configured as an LED similarly to the light-emitting portions 29 and 39may be provided in the housing 51 of the charger 50. The light-emittingportion 59 may be caused to light or to flash while power is beingsupplied from the interface portion 107 of the computer main unit 11 tothe charger 50. In this case, in step S5 of the charging controlprocessing (FIG. 8), the light-emitting portion 59 is caused to light orto flash when power supply to the charger 50 is started, and thelight-emitting portion 59 is extinguished when power supply to thecharger 50 is stopped in step S6.

Alternatively, the light-emitting portion 59 may be caused to light orto flash when power is received from the interface portion 107 of thecomputer main unit 11, separately from the charging control circuit 55of the charger 50. In this case, when in step S3 of the charging controlprocessing, the CPU 101 receives a charging request from the tablet 20,and power is supplied from the interface portion 107 to thelight-emitting portion 59.

In all of the above examples, the user is notified of the need to chargethe position indicator 30 through the lighting or flashing of thelight-emitting portion 59, permitting the user to promptly charge theposition indicator 30.

In the above first embodiment, an example was explained in which thecomputer main unit 11 supplies power to the charger 50 when the chargingrequest data transmitted from the position indicator 30 is “1”; but theinvention is not limited to such a configuration. For example, controlmay be executed in which power is supplied to the charger based on thetime elapsed since the previous charging. Below, such cases areexplained as modified examples 1 and 2 of this embodiment.

Modified Example 1

FIG. 11 is a flowchart showing charging control processing in a modifiedexample of the above first embodiment. The configuration of thismodified example is similar to that of the computer system 10 of theabove first embodiment, except for the operation of charging controlprocessing.

In the charging control processing shown in FIG. 11, the CPU 101 of thecomputer main unit 11 counts the time elapsed from the previous chargingof the position indicator 30 (step S11), and when this elapsed time hasreached a prescribed time (step S11: Yes), a charging request message isdisplayed on the monitor 12 (step S12), and causes the supply of powerfrom the interface portion 107 to the charger 50 to be started (stepS13). Then, after a prescribed time has elapsed, the CPU 101 stops thesupply of power to the charger 50 (step S14), returns to step S11, andcounts the elapsed time.

In this case, even when the tablet 20 has not received charging requestdata from the position indicator 30, the user is prompted to charge theposition indicator 30. Hence when charging request data is not receivedfrom the position indicator 30, the user can still be informed of theneed to charge the position indicator 30. Situations in which thecharging request data cannot be received may include, for example, whenthe voltages on the electrical double-layer capacitor 403 and capacitor405 have fallen to extremely low levels and the controller 401 cannotoperate at all, or when some obstacle exists or the distance between theposition indicator 30 and tablet 20 is too great, so that data cannot betransmitted from the position indicator 30 to the tablet 20.

Modified Example 2

FIG. 12 is a flowchart showing charging control processing in anothermodified example of the above first embodiment. The configuration ofthis modified example is similar to that of the system 10 of theabove-described first embodiment, except for the operation of chargingcontrol processing.

In the charging control processing shown in FIG. 12, the CPU 101 of thecomputer main unit 11 counts the time elapsed from the previous chargingof the position indicator 30 (step S21). When this elapsed time hasreached a prescribed time (step S21: Yes), the CPU 101 determineswhether the tablet 20 is able to receive signals transmitted from theposition indicator 30 (step S22).

When no signals transmitted from the position indicator 30 are beingreceived by the tablet 20 (step S22: No), the controller 401 displays acharging request message on the monitor 12 (step S23) and starts thesupply of power from the interface portion 107 to the charger 50 (stepS24). After a prescribed time has elapsed, the controller 401 stops thesupply of power to the charger 50 (step S25), and returns to step S21 tobegin counting elapsed time.

On the other hand, when after the prescribed time has elapsed from theprevious charging, signals from the position indicator 30 are receivedby the tablet 20 (step S22: Yes), the controller 401 determines whethersignals received by the tablet 20 comprise the charging request data “1”(step S26). When the charging request data “1” is present (step S26:Yes), the controller 401 proceeds to step S23 and causes charging to beperformed. On the other hand, when the charging request data “1” is notpresent (step S26: No), the controller 401 returns to step S21.

In the example shown in FIG. 12, even when charging request data is notreceived by the tablet 20 from the position indicator 30, the user canbe prompted to charge the position indicator 30. For example, even whencharging request data cannot be received from the position indicator 30,the user can be made to charge the position indicator 30 to return to astate in which use is possible. Further, when signals are transmittedfrom the position indicator 30 to the tablet 20 and moreover there is nocharging request data “1” from the position indicator 30 even after theprescribed time has elapsed from the previous charging, that is, whenadequate charge remains on the electrical double-layer capacitor 403 inthe position indicator 30, no charging is performed, and so unnecessarycharging can be avoided.

In the above first embodiment and modified examples, configurations wereexplained in which the supply of power to the charger 50 is started andstopped under control of the CPU 101. However, the invention is notlimited to such a configuration, and for example a switch may beprovided on the charger 50. Such a case is explained as a secondembodiment.

Second Embodiment

FIG. 13A shows an oblique, cross-sectional view of a charger 50A (stand)of a second embodiment of the invention, and FIG. 13B is a functionalblock diagram for operation of the charger 50A.

The computer system 10 of this second embodiment has a configurationcommon with that of the above first embodiment except for the charger50A shown in FIG. 13A, and so common portions are omitted from thedrawings and the detailed description hereinbelow.

As best shown in FIG. 13A, the charger 50A of this second embodiment isprovided with a detection switch 56 in the portion between the innerside of the insertion opening 52 and the inside of the support portion53. The detection switch 56 is configured so as to move when pressure isapplied, and an internal electrical contact is closed upon movement ofswitch 52 to a closed position.

As shown in FIG. 13B, the detection switch 56 is connected to thecharging control circuit 55. The charging control circuit 55 passes acurrent to the power supply coil 54 only in the state in which thedetection switch 56 is closed.

In this configuration, when the position indicator 30 (FIG. 2) isinserted into the insertion opening 52 of the charger 50A, the detectionswitch 56 is pressed by the case 31, and current begins to be suppliedto the power supply coil 54. In this state, an AC magnetic field isgenerated by the power supply coil 54 in the vicinity of the positionindicator 30, and an induced voltage appears in the coil 412 (FIG. 3),so that the electrical double-layer capacitor (FIG. 3) is charged. Whenthe position indicator 30 is removed from the insertion opening 52,current to the power supply coil 54 is stopped. Hence, when charging theposition indicator 30, it is sufficient to insert the position indicator30 into the insertion opening 52, wait for a prescribed length of time(for example, approximately 10 to 50 seconds), and then remove theposition indicator 30.

In this case, even when power is constantly supplied to the charger 50Afrom the computer main unit 11, current is passed to the power supplycoil 54 only when the position indicator 30 is actually set in thecharger 50A and the position indicator 30 is being charged, so thatunnecessary power consumption can be avoided. Further, there is nolonger a need for the computer main unit 11 to control current flow tothe charger 50A, so that more efficient control is possible.

In the above first and second embodiments and in the modified examples,configurations were described in which the position indicator 30 wascharged by chargers 50, 50A; but a tablet which integrates the functionsof these chargers 50, 50A can be used as explained below with regard tothird and fourth embodiments of the invention.

Third Embodiment

FIG. 14 is an oblique view showing the tablet 61 of a third embodimentof the invention.

The computer system 10 of this third embodiment comprises the tablet 61shown in FIG. 14 in place of the tablet 20 and charger 50 shown inFIG. 1. Except for this tablet 61, the configuration of the computersystem 10 is common to that of the above first embodiment, and so commonportions are omitted from the drawings and the detailed descriptionprovided hereinbelow.

The tablet 61 shown in FIG. 14 has a configuration in which an inputarea 61A is provided on the upper face of a substantially planarhousing. The tablet 61 incorporates an internal circuit 21 (FIG. 4)similar to that of the tablet 20, and in the input area 61A are embeddedloop coil groups 21A, 21B. On the outside of the input area 61A ispositioned a charging portion 62 (stand) on the upper face of the tablet61. The charging portion 62 has an outer casing which is substantiallydome-shaped, and an insertion opening 63 is formed integrally in theupper end of this outer casing. The insertion opening 63 has a diameterenabling insertion of at least the tip portion of the position indicator30 (FIG. 2), and is connected to a hole extending to the interior of thecharging portion 62.

The charging portion 62 incorporates a power supply coil 54 (FIG. 6) andcharging control circuit 55 (FIG. 6) similar to the charger 50. Thepower supply coil 54 is wound around the outside of the hole connectedto the charging portion 62.

when current is supplied to the power supply coil 54 incorporated intothe charging portion 62, by inserting the position indicator 30 into theinsertion opening 63, an AC magnetic field is generated in the vicinityof the coil 412 (FIG. 3) of the position indicator 30. The electricaldouble-layer capacitor 403 (FIG. 4) is charged by the current flowing inthis coil 412 which is induced by the AC magnetic field.

That is, the tablet 61 combines the functions of the tablet 20 forperforming position input operations using the position indicator 30 andthe functions of the charger 50 to perform charging of the positionindicator 30. Hence, according to this third embodiment, advantageouslythe computer system 10 can be installed in a smaller space. Further, thecomputer main unit 11 and tablet 61 can be connected by what appears tobe a single cable, so that cable layout is simplified, thereby easinginstallation.

Fourth Embodiment

FIG. 15 is an oblique view showing the configuration of the tablet 65 ofa fourth embodiment of the invention.

The computer system 10 of this fourth embodiment comprises the tablet 65shown in FIG. 15 in place of the tablet 20 and charger 50 shown inFIG. 1. Except for this tablet 65, the configuration of the computersystem 10 is common to that of the above first embodiment, and so commonportions are omitted from the drawings and detailed description providedhereinbelow.

The tablet 65 shown in FIG. 15 has a configuration in which an inputarea 65A is provided on the upper face of a substantially planarhousing. The tablet 65 incorporates an internal circuit 21 (FIG. 4)similar to that of the tablet 20, and in the input area 65A are embeddedloop coil groups 21A, 21B. On the outside of the input area 65A isembedded a power supply coil 66 (AC magnetic field generation unit) forthe tablet 65. The power supply coil 66 is, for example, a loop coilpositioned in a plane parallel to the upper face of the tablet 65, andmore specifically, is mounted by means of a printed board or similarstructure having a plurality of layers.

The tablet 65 incorporates a charging control circuit 55 (FIG. 6)similar to that of the charger 50. The charging control circuit 55 isconnected to the power supply coil 66. Hence an AC voltage is applied tothe power supply coil 66 under control of the charging control circuit55, and an AC magnetic field appears in the direction perpendicular tothe plane of the power supply coil 66.

According to this configuration, by incorporating the charging controlcircuit 55 in the tablet 65, when the tip of the position indicator 30,that is, the coil 412 (FIG. 4), is brought close to the power supplycoil 66 when current is being supplied to the power supply coil 66, anAC magnetic field is generated in the vicinity of the coil 412. Theelectrical double-layer capacitor 403 (FIG. 4) is charged by the currentflowing in the coil 412 induced by this AC magnetic field. Hence merelyby performing the simple operation of, for example, standing orotherwise positioning the position indicator 30 above the power supplycoil 66, the position indicator 30 can be charged.

Further, the tablet 65 combines the functions of the tablet 20 toperform position input operations using the position indicator 30 andthe functions of the charger 50 to charge the position indicator 30.Consequently, the system 10 advantageously can be installed in a smallerspace. Further, the computer main unit 11 and tablet 65 can be connectedby what appears to be a single cable, so that cable layout issimplified, and installation is made easier.

It is of course possible to provide, by printing or other means, adisplay on the upper face of the tablet 65 indicating the location inwhich the power supply coil 66 is embedded, and to provide guidance, ina charging request message displayed on the monitor 12, for charging theposition indicator 30 using this printed display as a guide.

Fifth Embodiment

FIG. 16 is an oblique view showing the configuration of the tablet-typecomputer 70 of a fifth embodiment of the invention.

The tablet-type computer 70 of this fifth embodiment is a portable-typecomputer incorporating a battery (not shown) as a power supply, and hasfunctions similar to those of the systems 10 in the above first throughfourth embodiments and in the modified examples.

The tablet-type computer 70 incorporates the control system 100 of thecomputer main unit 11 in a substantially board-shaped case 71. A liquidcrystal display panel 72 (display device) is positioned on the surfaceof the case 71, and below the liquid crystal display panel 72 is housedan internal circuit 21 (FIG. 4) incorporated within the tablet 20, withloop coil groups 21A, 21B embedded. That is, the liquid crystal displaypanel 72 also functions as an input area, and position input operationsusing the position indicator 30 can be performed on the liquid crystaldisplay panel 72.

Further, the functional configuration of the tablet-type computer 70 issimilar to that of the control system 100 of the computer main unit 11in FIG. 7, and various basic control programs and application programsare executed based on input operations by the position indicator 30.

An indicator housing portion 73 which houses the position indicator 30(FIG. 2) is formed in the case 71 of the tablet-type computer 70. Theindicator housing portion 73 is a tube-shaped structure, linked to aninsertion opening 74 which opens onto a side face of the case 71. Thedepth and inner diameter of the insert opening 74 are sized to enablehousing of the case 31 of the position indicator 30. Hence by insertingthe position indicator 30 into the insertion opening 74, the positionindicator 30 can be housed within the indicator housing portion 73.Further, a power supply coil 75 (AC magnetic field generation unit) iswound around the outside of the region of the indicator housing portion73 housing the tip portion of the position indicator 30. An AC voltageis applied to the power supply coil 75 by a charging control circuit,not shown. By use of this AC voltage, an AC magnetic field is generatedwithin the indicator housing portion 73.

In the tablet-type computer 70 configured as described above andillustrated in FIG. 16, when the position indicator 30 is not in use andis housed in the indicator housing portion 73, the position indicator 30is charged. Hence the position indicator 30 is maintained in aconstantly charged state, and there is the advantage that the positionindicator 30 can be used simply by removal from the indicator housingportion 73. Further, while there is a limit to the capacity of thebattery in the tablet-type computer 70, if, as in the above firstembodiment and modified examples, current is supplied to the powersupply coil 75 only when the position indicator 30 must be charged,power consumption can be greatly reduced, with no effect on theavailability for use of the tablet-type computer 70.

In the tablet-type computer 70, the position indicator 30 and the loopcoil groups 21A, 21B are opposed on either side of the liquid crystaldisplay panel 72, and there is the possibility that signals transmittedfrom the position indicator 30 may be affected by electromagnetic noise.But because, as described above, the position indicator 30 can transmitsignals efficiently and at high power, signals from the positionindicator 30 can be received satisfactorily by the loop coil groups 21A,21B. As a result, positions input using the position indicator 30 can bedetected precisely and with stability, and satisfactory operability issecured.

In the above first through fifth embodiments and the modified examples,examples were explained in which a method of generating an AC magneticfield in the vicinity of the coil 412 was used as the method of chargingthe electrical double-layer capacitor 403 incorporated within theposition indicator 30. But the invention is not limited to such amethod. For example, exposed terminals electrically connected to bothends of the electrical double-layer capacitor 403 may be provided in thecase 31, so that by connecting the exposed terminals to a power supplydevice external to the position indicator 30, the electricaldouble-layer capacitor 403 can be charged.

Further, in the above first through fifth embodiments and the modifiedexamples, an electrostatic coupling method may be used to detect theposition of the position indicator 30 using the tablet 20.

Below, an example of this is explained as a sixth embodiment.

Sixth Embodiment

FIG. 17 shows the configuration of the internal circuit 43 of theposition indicator of a sixth embodiment. FIG. 18 shows theconfiguration of the internal circuit 44 in the tablet of the sixthembodiment. In the internal circuit 43 and internal circuit 44 shown inFIG. 17 and FIG. 18, respectively, portions which are configuredsimilarly to those in the internal circuit 40 (FIG. 3) and the internalcircuit 21 (FIG. 4) are assigned the same symbols, and explanationsprovided above are not repeated below.

In this sixth embodiment, the position indicator 30 incorporating theinternal circuit 43 and the tablet 20 incorporating the internal circuit44 perform detection of indicated positions by electrostatic coupling. Anon-equilibrium signal voltage is applied as a reference to the tipconductor 434 of the conductive core 435, as best shown in FIG. 17,which protrudes from the tip of the case 31 (FIG. 2) in the positionindicator 30. When an operation is performed in which this conductivecore 435 is brought into contact with the surface of the tablet 20, thatis, with the input area 20A (FIG. 1), loop coils in the tablet 20 areelectrostatically coupled with the conductive core 435. Here, apotential difference appears at each loop coil in the tablet 20, andthese potential differences correspond to the distance from theconductive core 435, so that the position of the conductive core 435 canbe detected based on the potential differences of a plurality of loopcoils.

The configuration of the internal circuit 43 in FIG. 17 is explained.

In the internal circuit 43, a voltage conversion circuit 431 (voltagesupply assistance unit) is connected in series between the electricaldouble-layer capacitor 403 and the power supply terminal Vcc of thecontroller 401. The voltage conversion circuit 431 is a circuit whichconverts the voltage across the electrical double-layer capacitor 403and supplies a power supply voltage to the Vcc terminal of thecontroller 401. If the rated power supply voltage of the controller 401is 1.5 V, and if the voltage across the electrical double-layercapacitor 403 is 2.5 V, then the voltage conversion circuit 431 stepsdown this voltage to 1.5 V, and applies the stepped-down voltage to thepower supply terminal Vcc. Also, when for example the voltage across theelectrical double-layer capacitor 403 falls to 0.5 V, the voltageconversion circuit 431 steps up this voltage to 1.5 V and supplies thestepped-up voltage to the power supply terminal Vcc.

Control signals from the terminal P1 of the controller 401 are input tothe voltage conversion circuit 431, and signals can be transmitted fromthe voltage conversion circuit 431 to the terminal P2 of the controller401. When a control signal is input from the terminal P1 of thecontroller 401, the voltage conversion circuit 431 detects the voltageacross the electrical double-layer capacitor 403, and outputs a signalindicating the voltage value to the terminal P2. In this manner, thecontroller 401 can determine whether charging of the electricaldouble-layer capacitor 403 is necessary.

In the internal circuit 43, a charging terminal 432 (power transmissionunit) is connected to the electrical double-layer capacitor 403. Thischarging terminal 432 comprises a contact point exposed from the case 31(FIG. 2) of the position indicator 30. This contact point is connectedto a power supply device external to the computer system 10. Hence theelectrical double-layer capacitor 403 is charged by this external powersupply device.

Upon receiving a power supply voltage from the electrical double-layercapacitor 403, the controller 401 applies a sinusoidal voltage from theterminal P0 to the conductive core 435 protruding from the tip of thecase 31 (FIG. 2), based on a clock pulse generated by an oscillator 421.A capacitor 433 is connected in series between the terminal P0 and theconductive core 435, and only a sine-wave component is applied to theconductive core 435. Here, a tip conductor 434 is positioned on theperiphery of the conductive core 435, and this tip conductor 434 isconnected to a GND terminal of the controller 401.

On the other hand, in the internal circuit 44 incorporated within thetablet 20, each of the loop coils of the loop coil groups 21A, 21B isconnected to the multiplexer 444, and this multiplexer 444 is connectedto a differential amplifier 441, band-pass filter (BPF) 442, and controlportion 443, as best shown in FIG. 18.

The differential amplifier 441 amplifies the differences in the inputsignals from each loop, connected via the multiplexer 444, and outputsthe result to the band-pass filter 442. After removal of noisecomponents from this signal by the band-pass filter 442, the signal isinput to the control portion 443. The control portion 443 detects theposition of the conductive core 435, that is, the position indicatedusing the position indicator 30, based on the input signal.

In this way, the invention can be applied in cases of position detectionusing an electrostatic coupling method. In such cases also, the internalcircuit 43 of the position indicator 30 has an electrical double-layercapacitor 403, and this electrical double-layer capacitor 403 can beused as a power supply to drive the controller 401, so that sufficientlystrong signals can be transmitted from the internal circuit 43, andmoreover battery replacement and other troublesome maintenance isunnecessary.

Further, when a charging terminal 432 to charge the electricaldouble-layer capacitor 403 is provided, as in the sixth embodiment, byconnecting a device which supplies a prescribed DC voltage as anexternal power supply device to the charging terminal 432, theelectrical double-layer capacitor 403 can be charged rapidly. Asexplained above, the electrical double-layer capacitor 403 can becharged in an extremely short time, and so the external power supplydevice need only be connected to the charging terminal 432 for a shorttime. Hence charging is easily performed, and there is no need toprovide a special mechanism or the like to maintain contact between theexternal power supply and the charging terminal 432, and the device caneasily be realized at extremely low cost.

In this sixth embodiment, the loop coil groups 21A, 21B may be embeddedin the tablet 20 as described above; however, loop coils which do notdetract from the viewability of the liquid crystal screen of the tablet20 may be positioned at the surface of the tablet 20. In this case,there is the advantage that the position indicated by the positionindicator 30 incorporating the internal circuit 43 can be detected morestably and reliably.

In the above first through sixth embodiments and the modified examples,the position indicator 30 has been illustrated and discusses as having apen-type case 31. The invention is not limited to such a configuration,and for example a configuration may be employed using an air-brush type,digitizer cursor type, or mouse-type position indicator or similar, asmaller indicator with a ring shape, or other suitable configurationsand designs. Moreover, the position of the coil 412 in the positionindicator 30, the position, shape and number of the switches 33 and 34,and other structural features are arbitrary and may be modified withoutdeparting from the principals of the invention, as may other details ofthe configuration be modified.

Seventh Embodiment

FIG. 19 of the accompanying drawings is a block diagram showing anarrangement of a position pointing device according to a seventhembodiment of the present invention. In the embodiments which willfollow, it is assumed that the position pointing device has two kinds offunctions: a pen-point function, characterized by an ability to writeinformation, and an eraser function, characterized by an ability toerase written information. These writing and erasing functions areapplicable to a variety of different colors and stroke thicknesses.Although the below description is restricted to dual-function positionpointing devices in the interest of brevity, it should be understoodthat the position pointing devices may be capable of performing three ormore functions. It should also be understood that other functions may bepracticed in addition to or as alternatives of writing and erasing.

As shown in FIG. 19, the position pointing device according to theseventh aspect of the present invention includes at its pen-point side asignal transmission unit composed of a position pointing coil 211 and anoscillation circuit 212 with an oscillation frequency f1. This positionpointing device further includes at its eraser side a signaltransmission unit composed of a position pointing coil 213 and anoscillation circuit 214 with an oscillation frequency f2. Also, theposition pointing device includes a timing circuit (oscillator) 215 togenerate a square-wave signal with a predetermined frequency of whichthe duty ratio is nearly 50%. An output signal from the timing circuit215 is directly supplied to the oscillation circuit 212 as a drivingsignal, and the output signal is also supplied through an inverter 216to the oscillation circuit 214.

In this circuit, electric power is supplied from a battery (not shown)to respective units of the circuit to permit operation of the respectiveunits. The timing circuit 215 is adapted to generate a clock signal witha frequency having a period sufficiently longer than the time requiredby the tablet side to detect coordinates of the position pointed by theposition pointing device, for example, a clock signal with a frequencyof approximately 100 Hz. Thus, when the clock signal from the timingcircuit 215 is held at a high level, the oscillation circuit 212 on thepen-point side may be operated. When on the other hand the clock signalis held at a low level, the oscillation circuit 214 on the eraser sidemay be operated. Accordingly, in this circuit, it is possible to reducepower consumption of the pen-point side or the eraser side, either ofwhich may be alternately de-energized when not in operation so that onlyone side is energized at a time.

More specifically, in the seventh embodiment of the present invention,primary factors affecting power consumption are electric power consumedby the oscillation circuit 212 and the position pointing coil 211connected to the oscillation circuit 212, and electric power consumed bythe oscillation circuit 214 and the position pointing coil 213 connectedto the oscillation circuit 214. On the other hand, according to theseventh embodiment of the present invention, because the pen-point sideand the eraser side are controlled so as to alternately operate, theside not in use is de-energized, and power consumption can be decreased.As a result, an operator is able to freely select the pen-point or theeraser when the position pointing device is in use, while reducing powerconsumption at the non-selected side. In this manner, the life of thebattery can be prolonged.

Eighth Embodiment

Next, FIG. 20 shows an arrangement of a position pointing deviceaccording to an eighth embodiment of the present invention. As shown inFIG. 20, the position pointing device according to the eighth embodimentof the present invention includes at its pen-point side a resonancecircuit 221 with a predetermined resonance frequency f2. The resonancecircuit 221 is composed of a coil 221 a and a capacitor 221 b. Also, theposition pointing device of FIG. 20 includes at its eraser side aresonance circuit 222 with a predetermined resonance frequency f0. Theresonance circuit is composed of a coil 222 a and a capacitor 222 b. Amicroprocessor, generally depicted by reference numeral 223 in FIG. 20,includes a ROM (read-only memory) and a RAM (random-access memory),although not shown, and this microprocessor 223 is able to operate inaccordance with previously-set predetermined programs.

Also, an oscillator 224 with the above-described frequency f0 isconnected to the microprocessor 223 to generate a driving clock signalof the microprocessor 223 and signals with the frequency f0 which areradiated from the resonance circuits 221 and 222. As a result, while thesignal with the above-described frequency f0 is outputted from aterminal P0 of the microprocessor 223 at predetermined timing, theoutput signal from the terminal P0 is supplied at any one time to onlyone of the resonance circuit 221 of the pen-point side and the resonancecircuit 222 of the eraser side.

In the embodiment illustrated in FIG. 20, detecting units 226 and 227are adapted to detect the pressure that the operator puts on the styluspen when touching the position detecting tablet with the stylus pen.This pressure will hereinafter be simply referred to as a “styluspressure” and the detecting units 226 and 227 will hereinafter bereferred to as a “stylus pressure detecting unit 226” and a “styluspressure detecting unit 227,” respectively. The stylus pressuredetecting units 226 and 227 are connected to the microprocessor 223.These stylus pressure detecting units 226 and 227 may output detectedstylus pressures in the form of 8-bit digital values and themicroprocessor 223 may be operated so as to regularly read these digitalvalues. The microprocessor 223 outputs a signal to control an analogswitch 225 to a terminal P1 based on the read signals. In FIG. 20,reference numerals 228 and 229 denote coupling capacitors, respectively.

Consequently, the analog switch 225 supplies a signal to the pen-pointside when the signal from the terminal P1 of the microprocessor 223 isheld at a low level, and analog switch 225 supplies a signal to theeraser side when the signal from the terminal P1 is held at a highlevel. In this circuit, respective units are supplied with and energizedby electric power from a battery, not shown. Accordingly, also in thiscircuit, power consumption by the sides which are alternatelyde-energized can be reduced. Thus, the operator can freely choosebetween the pen-point side and the eraser side when the positionpointing device is in use. Also, power consumption can be decreased andlife of the battery can be prolonged by de-energizing the unselected(pen-point or eraser) side.

FIG. 21 is a cross-sectional view partially in perspective showing aspecific arrangement of a position pointing stylus pen which may serveas the above-mentioned position pointing device of the eighth embodimentof the present invention. As shown in FIG. 21, a pen-point 230 isprovided at the lower left end portion of FIG. 21 and an eraser 231 isprovided at the upper right end portion of FIG. 21. It should be notedthat the illustrated pen-point 230 and eraser 231 imitate writinginstrument components. The pen point 230 and eraser are preferablyformed of resin materials. Coils 221 a and 222 a, which serve asposition pointing coils, are provided in the vicinity of the pen-point230 and eraser 231, respectively.

The pen-point 230 and eraser 231 are connected at their inner endportions to the stylus pressure detecting units 226 and 227,respectively. Stylus pressures obtained when the pen-point 230 and theeraser 231 are depressed are transmitted to the stylus pressuredetecting units 226 and 227 and thereby the stylus pressures can bedetected. Then, the thus detected stylus pressures are converted into8-bit digital values, for example, and supplied to the microprocessors223 (not shown in FIG. 21) provided on a circuit board 232. It should benoted that the illustrated position pointing stylus pen includes abuilt-in battery 233 to supply electric power to suitable units such asthe microprocessor 223 on the circuit board 232.

Operations of the position pointing device according to the eighthembodiment of the present invention will be described with reference towaveform diagrams of FIGS. 22A, 22B and 22C.

FIG. 22A is a diagram of a waveform of signals to which reference willbe made in explaining operations of the position pointing device whenthe operator operates the pen-point side. The microprocessor 223 readsoutput data from the stylus pressure detecting unit 226. If the styluspressure of the pen-point side is greater than a predetermined styluspressure, then the microprocessor 223 fixes the terminal P1 at a lowlevel and outputs a signal from the terminal P0 at timing shown in FIG.22A. This signal outputted from the terminal P0 is a signal with afrequency nearly equal to the resonance frequency f0 of the resonancecircuit 221 as mentioned hereinbefore. This signal is intermittentlytransmitted at the cycle of 150 μs after the continuous transmissionperiod in which the above signal is continuously transmitted during theperiod longer than a constant period.

This intermittent transmission period occurs 9 times per cycle in which1 bit to distinguish the pen-point side and the eraser side is added to8 bits of stylus pressure information, i.e., 9 bits in total aretransmitted consecutively. As shown in FIG. 22A, according to thisembodiment, a signal is transmitted if transmitted data is “0” and asignal is not transmitted if transmitted data is “1”. Thus, “0” or “1”may be represented. Accordingly, the tablet side is able to receivesignals in accordance with these timings and it is able to detecttransmitted data from the position pointing device in response to “0”obtained if a signal is detected and “1” obtained if a signal is notdetected.

Also, FIG. 22B is a diagram of waveforms of signals to which referencewill be made in explaining operations of the position pointing devicewhen the operator operates the eraser side. The microprocessor 223 readsoutput data from the stylus pressure detecting unit 227. If the styluspressure of the eraser side is greater than a predetermined styluspressure, then the microprocessor 223 fixes the terminal P1 at a highlevel and outputs a signal from the terminal P0 at timing shown in FIG.22B. This signal is supplied to the resonance circuit 222 (FIG. 2) atexactly the same timing as that shown in FIG. 22A and then it isradiated. The operations shown in FIG. 22B differ from the operations ofthe pen-point side shown in FIG. 22A only in that the final bit of thetransmitted data is “1”.

Consequently, the tablet side is able to determine that the receivedresult of this final data is “1” and further is able to recognize thatthe received signal should be transmitted from the eraser side.

FIG. 22C is a diagram of signal waveforms to which reference will bemade in explaining operations of the position pointing device when thestylus pressure detects, for both the pen-point side and the eraserside, results that are less than the predetermined value. The positionpointing device may alternately carry out the operations of thepen-point side (FIG. 22A) and the operations of the eraser side (FIG.22B) by alternately switching the terminal P1 to the high level and thelow level. However, 8 bits of stylus pressure information shown in FIG.22C are all “0”.

As described above, according to this embodiment, because the one-bitportion of the signal is intermittently transmitted after the continuoustransmission period in which the 8-bit portion of the signal iscontinuously transmitted during a time period longer than the constanttime, the tablet side is able to easily operate with timing matched withthat of the position pointing device. Also, the pen-point side and theeraser side can be distinguished from one another by only one frequency.The pen-point side and the eraser side are alternately operated when theoperator operates neither the pen-point side nor the eraser side.Accordingly, the tablet side is able to detect which of the pen-pointside or the eraser side is operated irrespective of which side isoperated first and hence the operator can choose from the pen-point andthe eraser freely when the position pointing device is in use.

In the above-mentioned position pointing device, a primary source of theconsumption of electric power is the electric power supplied to andconsumed by the resonance circuits 221 and 222 from the terminal P0 ofthe microprocessor 223 through the analog switch 225. This problem islargely overcome by the present embodiment. Because at any time only oneof the resonance circuits 221 or 222 is energized and the other isde-energized under control of the analog switch 225, power consumptionof the position pointing device can be decreased and life of the batterycan be prolonged.

When the pen-point side stylus pressure and the eraser side styluspressure both are less than a predetermined value, the position pointingdevice may, after a given or predetermined time period, move to thealternate operations mode shown in FIG. 22C. The reason for movement tothe alternate operations mode is that, when the position pointing deviceis in ordinary use, the operator is unable to suddenly switch thepen-point side to the eraser side. In actual manipulation, the operatormay frequently and repeatedly use the position pointing device in such amanner as to operate the pen-point side or the eraser side with orwithout stylus pressure greater than the constant value. As a result ofthe alternate operations mode, the operator is able to operate theposition pointing device smoothly.

Further, while the pen-point side and the eraser side are switched undercontrol of the analog switch 224 in this embodiment of the presentinvention, the present invention is not limited thereto. For example,the microprocessor 223 may include two terminals by which the signalwith the frequency f0 can be outputted and the signal may be outputtedfrom either one of the two terminals. In that case, the microprocessor223 may switch therein the outputs to the two terminals by using thesignal outputted to the terminal P1. In this case, extra analog switch225 need not be provided and the microprocessor 223 may have the samenumber of terminals as sides.

While switching between the pen-point side and the eraser side is basedon detections of the stylus pressures in the above-described eighthembodiment of the present invention, the present invention is notlimited thereto. Switching can be switched based on other detectors, asdescribed below.

Ninth Embodiment

FIG. 23 shows an arrangement of a position pointing device according toa ninth embodiment of the present invention using touch-sensitivesensors as the above-mentioned detectors. In FIG. 23, elements and partsidentical to those of FIG. 20 are denoted by identical referencenumerals and therefore the description of common features is notrepeated hereinbelow.

Specifically, as shown in FIG. 23, the position pointing deviceaccording to this ninth embodiment includes electrodes 234 and 235serving as touch-sensitive sensors, and square-wave output signals aresupplied from the terminals P2 and P4 of the microprocessor 236 to theseelectrodes 234 and 235, respectively. The electrodes 234 and 235 areconnected to terminals P3 and P5, respectively, of the microprocessor236 and thereby electric potential is detected. Also in this circuit,electric power is supplied from a battery, not shown, and therebyrespective units of the microprocessor 236 and the like can be operated.

Examples of the operation of this ninth embodiment of the presentinvention are described below. If the operator's hand is not near theelectrode 234, then the square-wave signal outputted from the terminalP3 is slightly deteriorated in waveform, as shown in FIG. 24A. Thisdeterioration is detected at the terminal P3. On the other hand, if theoperator's hand is near the electrode 234, then the square-wave signaloutputted from the terminal P2 is considerably deteriorated in waveform,as shown in FIG. 24B, and the deterioration is detected at the terminalP3. Accordingly, it is possible for the microprocessor 236 by analyzingthe change of the waveform to determine which of the electrodes 234 and235 is near the hand of the operator.

FIG. 25 is a perspective view showing an example of a position pointingstylus pen 239 serving as the above-mentioned position pointing deviceof the ninth embodiment of the present invention. Specifically, as shownin FIG. 25, the position pointing stylus pen 239 includes theabove-mentioned electrodes 234 and 235 provided near the pen-point 230and the eraser 231, respectively. The electrode 234 is positioned wherethe fingers of the operator grip the position pointing stylus pen 239for writing mode, and the electrode 235 is situated where the fingers ofthe operator grip the position pointing stylus pen 239 for erasing mode.The remainder of the inside structure of this position pointing styluspen 239 is substantially equivalent to the position pointing stylus pendescribed above, e.g., in which the microprocessor 236 is provided onthe circuit board 235, with the exception that the stylus pressuredetecting units 226 and 227 present in the arrangement shown in FIG. 21are excluded and therefore need not be illustrated and described withrespect to this embodiment.

Accordingly, in the ninth embodiment of the present invention, when theoperator operates the position pointing device 239 to employ thepen-point 230 or the eraser 231, the location at which the operator'sfingers grip the device 239, i.e., near the electrode 234 or 235,determines the side of the device 239 which is being used on the tablet.As a result, the position pointing device 239 can execute processingoperations similar to those described above with reference to FIGS. 22A,22B, and 22C. It should be noted that the direction of the pen-point 230or the eraser 231 can be determined by changing the oscillationfrequency.

Tenth Embodiment

Further, FIG. 26 is a block diagram showing an arrangement of a positionpointing device according to a tenth embodiment of the presentinvention. In the following description with reference to FIG. 26,elements and parts identical to those of FIG. 20 are denoted byidentical reference numerals.

Specifically, as shown in FIG. 26, the pen-point side includes theresonance circuit 221 with the predetermined resonance frequency f0. Theresonance circuit 221 includes the coil 221 a and the capacitor 221 b.The eraser side includes the resonance circuit 222 with thepredetermined frequency f0. The resonance circuit 222 includes the coil222 a and the capacitor 222 b. Further, a microprocessor, generallydepicted by reference numeral 240 in FIG. 26, includes a ROM (read-onlymemory) and a RAM (random-access memory), although not shown. Themicroprocessor 240 can be operated in accordance with previously-setpredetermined programs.

Also, the oscillator 224 with the above-described frequency f0 isconnected to this microprocessor 240 to generate a driving clock signalof the microprocessor 240 and to generate the signal with the frequencyf0 which is to be radiated from the resonance circuits 221 and 222. As aconsequence, the signals with the above-described frequency f0 areoutputted from the terminals P0 and P6 of the microprocessor 240 atpredetermined timings, and the output signals from these terminals P0and P6 are supplied through capacitors 228 and 229, respectively, to thepen-point side resonance circuit 221 and the eraser side resonancecircuit 222, respectively.

Further, capacitors 241 and 242 are respectively connected to theabove-mentioned capacitors 228 and 229, and analog switches 243 and 244are respectively connected to the capacitors 241 and 242 in series. Theanalog switches 243 and 244 are driven under control of the signals fromthe terminals P1 and P7 of the microprocessor 240. It should be notedthat the analog switches 243 and 244 are respectively energized when thesignals from the terminals P1 and P7 of the microprocessor 240 are heldat a high level.

The microprocessor 240 is connected to the stylus pressure detectingunit 226 for detecting the stylus pressure obtained when the operatoroperates the position pointing device at its pen-point side. Themicroprocessor 240 is also connected to the stylus pressure detectingunit 227 for detecting the stylus pressure obtained when the operatoroperates the position pointing device at its eraser side. These styluspressure detecting units 226 and 227 each are adapted to output detectedstylus pressures in the form of 8-bit digital values, and themicroprocessor 240 is adapted to regularly read these values. Themicroprocessor 240 outputs signals to control the analog switches 243and 244 to the terminals P1 and P6 based on the read out signals.

When the signal from the terminal P1 of the microprocessor 240 is heldat a low level, the analog switches 243 and 244 allow the capacitors 228and 241 to be connected in parallel to each other to thereby raise thesignal supplied to the resonance circuit 221 of the pen-point side inlevel. When the signal from the terminal P7 of the microprocessor 240 isheld at a low level, the analog switches 243 and 244 allow thecapacitors 229 and 242 to be connected in parallel to each other tothereby raise the signal supplied to the resonance circuit 222 of theeraser side in level. It should be noted that, also in the circuit shownin FIG. 26, electric power for operation of the units is supplied from abattery (not shown) to the respective units.

Operations of the position pointing device having the above-mentionedarrangement according to the tenth embodiment of the present inventionwill be described below. The signal with the frequency f0 is outputtedfrom the terminal P0 of the microprocessor 240 at the same timing asthat shown in FIG. 22A, and the signal is supplied through the capacitor228 to the resonance circuit 221. In a like manner, the signal with thefrequency f0 also is outputted from the terminal P6 of themicroprocessor 240 at the same timing as that shown in FIG. 22B and thesignal is supplied through the capacitor 229 to the resonance circuit222. The signals from these terminals P0 and P6 are outputted at thesame time and the signal with the frequency f0 is constantly supplied tothe resonance circuits 221 and 222.

Then, in this embodiment, the detected result obtained by the styluspressure detecting unit 226 is transmitted from the terminal P0 and thedetected result obtained by the stylus pressure detecting unit 227 istransmitted from the terminal P6. While the signals are transmitted fromboth of the pen-point side and the eraser side, the tablet is able todetect a signal with the higher level from either the pen-point side orthe eraser side.

In this embodiment, the capacitor 241 is connected in parallel to thecapacitor 228 through the analog switch 243. Similarly, the capacitor242 is connected in parallel to the capacitor 229 through the analogswitch 244. Further, the microprocessor 240 regularly reads an outputvalue from the stylus pressure detecting unit 226 that detects pressureof the pen-point applied when the operator operates the positionpointing device at its pen-point side, and an output value from thestylus pressure detecting unit 227 that detects pressure of the eraserapplied when the operator operates the position pointing device at itseraser side.

Accordingly, if the stylus pressure of the pen-point side (output valuefrom the stylus pressure detecting unit 226) is greater than apredetermined value, then the microprocessor 240 sets the terminal P1 toa high level to energize the analog switch 243. As a result, capacitivecoupling generated when the signal outputted from the terminal P0 issupplied to the resonance circuit 221 is increased. Power of the signaltransmitted from the resonance circuit 221 is thereby increased.

On the other hand, if the stylus pressure of the eraser side (outputvalue from the stylus pressure detecting unit 227) is greater than apredetermined value, then the microprocessor 240 sets the terminal P7 toa high level to energize the analog switch 244. As a result, capacitivecoupling generated when the signal outputted from the terminal P6 issupplied to the resonance circuit 222 is increased. Power of the signaltransmitted from the resonance circuit 222 is thereby increased.

Accordingly, in this embodiment, transmission power of the operated sidecan be increased by the aforementioned operations and hence it ispossible for the tablet side to detect a signal stably. Also, becausepower of the side which is not operated can be suppressed to theminimum, power consumption can be decreased and life of the battery canbe prolonged. It should be noted that, if the stylus pressure of oneside is greater than a predetermined value, then transmission of asignal from the other side may be stopped completely.

However, in this embodiment, if transmission of a signal from one sideis stopped completely, then when the position pointing device is quicklyswitched in operation from the pen-side to the eraser side or viceversa, a problem arises. Specifically, the tablet side becomes unable todetect a signal obtained immediately after switching from one side toanother, because the side switched to is not sending any signal. Thatis, the position pointing device experiences a delay in the recognitionof the switch operation. However, if a signal is transmitted with smallpower from the side not in operation, then the position pointing devicecan manage the above-mentioned quick switching of operation and hencethe device can recognize switching of operation immediately. It shouldbe noted that, although stability of detected coordinates is loweredduring the first very short time period, stability of detectedcoordinates can be improved as the position pointing device transitionsto ordinary power.

Eleventh Embodiment

FIG. 27 is a block diagram showing arrangements of a position inputsystem and a computer system according to an eleventh embodiment of thepresent invention. The position input system and computer system of FIG.27 are compatible with the position pointing devices of variousembodiments described above, including, but not necessarily limited to,the seventh to tenth embodiments.

As best shown in FIG. 27, the position detecting apparatus according tothis embodiment includes a sensor coil group 201 composed of a pluralityof loop coils, for example. In this sensor coil group 201, in order todetect the position in the X-axis direction and the position in theY-axis direction, long sides of loop coils (shown by only lines forsimplicity) for effecting electromagnetic induction are provided so asto cross each other as shown in FIG. 27. It should be noted thatsolid-line (X-axis) loop coils and broken-line (Y-axis) loop coils inFIG. 27 are provided on different layers. The position pointing pen 239having the above-mentioned pen-point 230 and eraser 231 is moved closeto the sensor coil group 201 when this position input system is in use.

Also, a plurality of loop coils forming the sensor coil group 201 issequentially provided in an overlapping fashion such that wirings ofcoils are provided at a predetermined pitch. Further, end portions ofthe loop coils in each layer are connected to a selecting circuit 204Xor a selecting circuit 204Y and hence those loop coils are sequentiallyselected, scanned and driven by the selecting circuit 204X or 204Y. Itshould be noted that the selecting circuit 204X or 204Y may select thoseloop coils in accordance with a control signal from a control circuit205. Accordingly, the control circuit 205 is able to constantlyrecognize the position of the loop coil selected within the sensor coilgroup 201.

A signal received at the loop coil selected by the above-mentionedselecting circuit 204X or 204Y is supplied through a common amplifier251 to a bandpass filter (BPF) 252 which passes the above-mentionedspecific frequency f0, and a signal passed through the bandpass filter252 is supplied to a detector 253. Further, a signal detected by thedetector 253 is supplied through a sample-and-hold (S/H) circuit 254 toan analog-to-digital (A/D) converter 255, and a signal, which wasconverted from an analog signal to a digital signal by the A/D converter255, is inputted to the control circuit 205. As a result, the controlcircuit 205 can recognize magnitude of a received signal and theposition of the loop coil which receives a signal.

Therefore, according to the arrangement shown in FIG. 27, the controlcircuit 205 can detect the position at which the position pointing pen239 is moved close to the sensor coil group 201 and can function as theposition detecting apparatus. Also, if the control circuit 205 isprovided as a central processing unit (CPU) for carrying out processingbased on an arbitrary program, then the position detecting apparatus canconstitute part of a computer system for carrying out processing fordetecting the position at which the position pointing pen 239 approachesthe sensor coil group 201. In this case, if the resonance circuits builtinto the position pointing pens 239 are operated one at a time under thecontrol of the control circuit 205, then power consumption can bedecreased and the life of the built-in battery can be prolonged.

As described above, the position pointing device of several of theabove-described embodiments of the present invention includes a built-inpower supply unit for transmitting a signal to point at least theposition to a position detecting tablet. This position pointing deviceincludes signal transmitting units provided at a plurality of portionsof the position pointing device and a control unit for controlling aplurality of signal transmitting units such that the units are in anenergized or de-energized state. Consequently, power consumption in theposition pointing device can be decreased and life of the built-inbattery can be prolonged.

Also, according to the position pointing device of several of theabove-described embodiments of the present invention, a built-in powersupply unit transmits a signal to point at least the position of theposition pointing device to a position detecting tablet. This positionpointing device includes signal transmitting units provided at aplurality of portions of the position pointing device and a powercontrol unit for controlling transmission power of a plurality of signaltransmitting units at least in two levels. Consequently, powerconsumption in the position pointing device can be decreased and life ofthe built-in battery can be prolonged.

Further, according to the position detecting apparatus of several of theabove-described embodiments of the present invention, the position inputsystem includes a position pointing device having a built-in powersupply unit to transmit a signal to provide positioning information to aposition detecting tablet, a plurality of signal transmitting unitsprovided at a plurality of portions, and a power control unit forcontrolling transmission power to a plurality of signal transmittingunits. The position detecting tablet includes a discriminating unit fordiscriminating signals from the plurality of signal transmitting units,and the position detecting apparatus outputs information based on thepositioning information from the position pointing device anddiscrimination information from the discriminating unit. Thus, powerconsumption in the position pointing device can be decreased and life ofthe built-in battery can be prolonged.

Furthermore, according to several of the above-described embodiments ofthe present invention, a computer system is provided which includes aposition pointing device having a built-in power supply unit to transmita signal identifying at least the position of the position pointingdevice relative to a position detecting tablet, signal transmittingunits provided at a plurality of portions, a power control unit forcontrolling transmission power to a plurality of signal transmittingunits, the position detecting tablet, and a computer. The positiondetecting tablet includes a discriminating unit for discriminating eachof signals from a plurality of signal transmitting units and thecomputer executes processing corresponding to positioning informationfrom the position pointing device and based on discriminationinformation from the discriminating unit.

It should be noted that the present invention is not limited to theabove-described embodiments. Also, the two functions—pen-point function(writing of information) and the eraser function (erasing of writteninformation) of this position pointing device—are compatible withwritten information of different colors and of different thickness.Furthermore, the position pointing device according to the variousembodiments of the present invention can include two, three, or morethan three functions, with each “side” operated alternately so that onlyone side is powered at an operational level at a time, and so that theother side(s) is either not powered or operated at a decreased power.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors, insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A position input system, comprising: a position indicator fortransmitting signals; and a position detector device for receivingsignals transmitted from the position indicator, wherein said positionindicator comprises an electrical double-layer capacitor, a chargingcircuit which charges the electrical double-layer capacitor, and a powertransmission unit which relays power supplied from a power supply unitexternal to the position indicator to said charging circuit.
 2. Theposition input system according to claim 1, wherein said power supplyunit is external to said position detector.
 3. The position input systemaccording to claim 2, wherein: a coil is in said position indicator, andsaid external power supply unit is an AC magnetic field generation unit.4. The position input system according to claim 3, wherein said powersupply unit comprises a stand housing said AC magnetic field generationunit, wherein the stand is configured to enable setting of said positionindicator.
 5. The position input system according to claim 4, whereinsaid stand comprises a detector switch for selectively supplying currentto said power supply unit only when said position indicator is receivedby said stand.
 6. The position input system according claim 3, whereinthe power supply unit is incorporated into said position detector devicefor permitting charging of the double-layer capacitor when said positionindicator is placed above said position detector device.
 7. The positioninput system according to claim 1, further comprising a power supplyassistance unit for receiving power from said electrical double-layercapacitor and supplying a prescribed voltage to said position indicator.8. The position input system according to claim 1, wherein said positiondetector device detects signals transmitted from said position indicatorbased on an electrostatic coupled state with said position indicator. 9.The position input system according to claim 1, wherein said positiondetector device detects signals transmitted from said position indicatorbased on electromagnetic coupling with said position indicator.
 10. Theposition input system according to claim 9, wherein said positionindicator comprises a resonance circuit comprising a coil and capacitor.11. The position input system according to claim 1, wherein saidposition indicator comprises: a voltage detection unit for detectingwhen the voltage across said electrical double-layer capacitor hasdropped to or below a prescribed voltage value, and an informationtransmission unit for transmitting information indicating the detectionof the drop in voltage by said voltage detection unit to said positiondetector device.
 12. A computer system, comprising: a position inputsystem comprising a position indicator for transmitting signals, and aposition detector device for receiving signals transmitted from theposition indicator; a display device; and a computer for processingpositions detected by said position input device, wherein said positionindicator comprises an electrical double-layer capacitor; a chargingcircuit for charging the electrical double-layer capacitor; and a powertransmission unit for relaying and supplying, to said charging circuit,power from a power supply unit external to the position indicator. 13.The computer system according to claim 12, further comprising: a voltagedetection unit for detecting when the voltage of said electricaldouble-layer capacitor has dropped to or below a prescribed voltagevalue; and an information transmission unit for transmitting to saidposition detector device information indicating detection of the voltagedrop by the voltage detection unit.
 14. The computer system according toclaim 13, further comprising an AC magnetic field generation unit assaid power supply unit, wherein a coil is provided in said positionindicator, and wherein said computer is operable, upon reception by saidposition detector device of the information indicating detection of thevoltage drop transmitted from said information transmission unit, tosupply current to said AC magnetic field generation unit.
 15. Thecomputer system according to claim 13, wherein the computer is operable,based on the information indicating detection of the voltage droptransmitted from said information transmission unit, to cause a reportto be displayed by said display device.
 16. The computer systemaccording to claim 13, further comprising an AC magnetic fieldgeneration unit as said power supply unit, wherein a coil is provided insaid position indicator, and wherein said computer is operable to supplycurrent to said AC magnetic field generation unit when a prescribed timehas elapsed from the previous supply of current to said AC magneticfield generation unit.
 17. The computer system according to claim 13,further comprising a prompt to notify a user, based on the informationindicating detection of the voltage drop transmitted from saidinformation transmission unit, to charge said electrical double-layercapacitor, wherein said prompt is located on the position indicator. 18.The computer system according to claim 13, further comprising a promptto notify a user, based on the information indicating detection of thevoltage drop transmitted from said information transmission unit, tocharge said electrical double-layer capacitor, wherein said prompt islocated on the position detector device.
 19. The computer systemaccording to claim 13, further comprising a prompt to notify a user,based on the information indicating detection of the voltage droptransmitted from said information transmission unit, to charge saidelectrical double-layer capacitor, wherein said prompt is located on thepower transmission unit.
 20. The computer system according to claim 13,further comprising an AC magnetic field generation unit as said powersupply unit, wherein a coil is provided in said position indicator, andwherein said computer is operable to supply current to said AC magneticfield generation unit when the information indicating detection of thevoltage drop transmitted by said information transmission unit is notreceived by said position detector device within a prescribed time fromthe previous passage of current to said AC magnetic field generationunit.
 21. The computer system according to claim 12, further comprisingan AC magnetic field generation unit as said power supply unit, whereina coil is provided in said position indicator, and wherein said computeris operable to issue a charging request and supply current to said ACmagnetic field generation unit when a prescribed time has elapsed fromthe previous supply of current to said AC magnetic field generationunit.
 22. The computer system according to claim 12, further comprisingan AC magnetic field generation unit as said power supply unit, whereina coil is provided in said position indicator, and wherein said powersupply unit comprises a detection switch which is activated when saidposition indicator is placed in a charging position with respect to saidpower supply unit.
 23. The computer system according to claim 12,wherein said power supply unit is integrated into said position detectordevice.
 24. A method of charging a position indicator of a positioninput system comprising the position indicator for transmitting signalsand a position detector device for receiving signals transmitted by theposition indicator, said method comprising the steps of: providing aposition indicator with an electrical double-layer capacitor, a chargingcircuit which charges the electrical double-layer capacitor, and a powertransmission unit; and supplying power from a power supply unit externalto the position indicator, and causing the power transmission unit torelay the power to the charging circuit.
 25. A method of operating acomputer system, comprising the steps of: providing a position inputsystem comprising a position indicator for transmitting signals, and aposition detector device for receiving signals transmitted from theposition indicator; providing a computer for processing informationbased on positions detected by said position input device; and supplyingpower from a power supply unit external to the position indicator, andcausing the power transmission unit to relay the power to the chargingcircuit.
 26. The method according to claim 25, including the furthersteps of: detecting when the voltage of the electrical double-layercapacitor has dropped to or below a prescribed voltage value; andtransmitting to the position detector device information indicatingdetection of the voltage drop.
 27. A position pointing device fortransmitting a positioning signal to a position detecting tablet, theposition pointing device comprising: An integrated power supply unit; aplurality of signal transmitting units provided at a plurality ofportions of a position pointing device; and a control unit for switchingsaid plurality of signal transmitting units between energized andde-energized states.
 28. A position pointing device according to claim27, wherein said plurality of signal transmitting units comprises firstand second signal transmitting units respectively provided at oppositeend portions of said position pointing device.
 29. The position pointingdevice according to claim 28, wherein said first and second signaltransmitting units transmit a pen-point signal and an eraser signal,respectively.
 30. A position pointing device according to claim 27,wherein said control unit alternately switches said signal transmittingunits between an energized state and a de-energized state.
 31. Aposition pointing device according to claim 27, further comprising: adirection detecting unit for detecting the direction in which saidposition pointing device is arranged relative to the position detectingtablet, and wherein said control unit energizes whichever of the signaltransmission units faces towards the position detector tablet based on adetected result of said direction detecting unit.
 32. A positionpointing device according to claim 31, wherein said direction detectingunit comprises a stylus pressure detecting unit, and wherein saidcontrol unit is operable to energize whichever of the signaltransmission units touches the position detector tablet based ondetection by the stylus pressure detecting unit of a load greater than apredetermined load.
 33. A position pointing device according to claim32, wherein said control unit is operable to sequentially operate saidplurality of signal transmitting units if it is determined by the styluspressure detecting unit that a load greater than said predetermined loadis not detected from any one of said plurality of signal transmittingunits.
 34. A position pointing device according to claim 31, whereinsaid direction detecting unit is a touch-sensitive sensor and saidcontrol unit is operable to energize whichever of said signaltransmission units is associated with an end of the position pointingdevice which touches the position detecting tablet.
 35. A positionpointing device for transmitting a positioning signal to a positiondetecting tablet, the position pointing device comprising: a built-inpower supply unit; a plurality of signal transmitting units provided ata plurality of portions of said position pointing device; and a powercontrol unit for switching magnitude of transmission power of saidsignal transmitting units between at least two power levels.
 36. Aposition pointing device according to claim 35, wherein first and secondsignal transmitting units of said plurality of signal transmitting unitsare disposed at opposite end portions of said position pointing deviceto transmit a pen-point signal and an eraser signal, respectively.
 37. Aposition pointing device according to claim 35, further comprising adirection detecting unit for detecting the direction of said positionpointing device relative to a position detecting tablet, wherein saidpower control unit is operable to increase, based on a detected resultof the direction detecting unit, a magnitude of transmission power fromwhichever of said signal transmitting units is located on a side of saidpositioning pointing device nearer to the position detecting tablet, sothat the magnitude of transmission power from said signal transmittingunit located on the side nearer to the position detecting tablet isgreater than a magnitude of transmission power from whichever of saidsignal transmitting units is on the opposite side of said positioningpointing device.
 38. A position pointing device according to claim 35,wherein said control unit alternately switches said signal transmittingunits between the energized state and the de-energized state.
 39. Aposition input system, comprising: a position pointing device fortransmitting positioning information signals, said position pointingdevice comprising a built-in power supply unit, a plurality of signaltransmitting units provided at a plurality of portions of said positionpointing device, and a power control unit for controlling transmissionpower of each of said plurality of signal transmitting units; a positiondetecting tablet for receiving the positioning information signals fromthe position pointing device; and a discriminating unit fordiscriminating the positioning information signals from said pluralityof signal transmitting units.
 40. A position input system according toclaim 39, wherein said discriminating unit comprises a firstdiscriminating unit provided at a first end portion of said positionpointing device to discriminate a pen-point signal, and wherein saidposition input system further comprises a second discriminating unitprovided at a second end portion of said position pointing device todiscriminate an eraser signal.
 41. A position input system according toclaim 39, wherein said control unit alternately switches said signaltransmitting units between the energized state and the de-energizedstate.
 42. A computer system, comprising: a position pointing device fortransmitting positioning signals, the position pointing devicecomprising a built-in power supply unit, a plurality of signaltransmitting units provided at a plurality of portions of said positionpointing device, and a power control unit for controlling transmissionpower of each of said plurality of signal transmitting units; a positiondetecting tablet for receiving the positioning signals from the positionpointing device; a discriminating unit for discriminating thepositioning signals from said plurality of signal transmitting units;and a computer for processing the positioning signals from said positionpointing device and discrimination information from said discriminatingunit.
 43. A computer system according to claim 42, wherein saiddiscriminating unit comprises a first discriminating unit provided at afirst end portion of said position pointing device to discriminate apen-point signal, and wherein said computer system further comprises asecond discriminating unit provided at a second end portion of saidposition pointing device to discriminate an eraser signal.
 44. Acomputer system according to claim 42, wherein said control unitalternately switches said signal transmitting units between theenergized state and the de-energized state.
 45. A method for charging aposition pointing device, comprising the steps of: providing a positionpointing device for transmitting a positioning signal to a positiondetecting tablet, the position pointing device comprising a built-inpower supply unit, a plurality of signal transmitting units provided ata plurality of portions of said position pointing device, and a controlunit; and switching said plurality of signal transmitting units betweenenergized or de-energized states.